World number one Ash Barty refused to criticise Karolina Muchova's reasoning for a medical timeout after she was surprisingly beaten in the Australian Open quarter-finals.

Barty's bid to become the first Australian woman to win the Melbourne grand slam since 1978 came to a shock end on Wednesday, upstaged by 25th seed Muchova 1-6 6-3 6-2.

Winner of the 2019 French Open, Barty raced through the opening set in 24 minutes and led 2-1 in the second before Muchova requested an off-court medical timeout on Rod Laver Arena.

It was a turning point, Muchova returning reinvigorated as the unheralded Czech reached her maiden major semi-final in remarkable fashion, with the 24-year-old revealing during her on-court interview, "I was a bit lost [gestures at head] on the court and my head was spinning so I took a break. It helped me.

"It was more they just checked my pressure because I was a bit lost. I was spinning. So they cooled me down a bit with ice and it helped me."

Asked about Muchova's actions, Barty told reporters: "It's within the rules. She's within her rights to take that time. If she wasn't within the rules, the physios and the doctors would have said so. That's the laws of our game, is that we have those medical timeouts for cases that are needed. Obviously she needed that today. Completely within the rules for her to take that.

"From my point of view, I've played a lot of matches where there have been medical timeouts. I've taken medical timeouts myself before, so that shouldn't be a massive turning point in the match. I was disappointed that I let that become a turning point. I'm experienced enough now to be able to deal with that. It's a disappointment today without a doubt. But we learn and we move on."

Barty added: "I would have liked to have just been a little bit sharper the next game. Started well with the first point, just made a couple loose errors in that game. I think for the rest of the set, that was the story, it was just over and over-made. Probably pressed a little bit trying to be overly aggressive.

"Had some break points, I think it was that three-all, that was probably a bit of a critical game in the momentum there for the second set. Just disappointed with the fact that I wasn't able to bring the match back on my terms after she took that break."

"I didn't hear what she said when she called for the trainer," Barty continued. "That's not my decision. When you call for the trainer, you obviously tell the umpire what the reason is. And then the doctor and physios come out and assess it. That's within the rules. For me, that's not really my decision and not my concern what she took the medical for.

"Obviously there are rules when we go off the court for whatever areas you're getting treated because that's quite normal. But, yeah, that's not really my decision to make on whether or what her medical condition was or what the timeout was for."

Brady, who tallied 31 unforced errors in the final two sets having only managed six in the first, said: "It's heartbreaking, of course. But will it deter me, will it ruin the fact we've had a really successful start to our season? Absolutely not.

"The sun will come up tomorrow. We go about our work again. You're either winning or you're learning. I think today is a massive learning curve for me, for Tyz [coach Craig Tyzzer], my team as well. We take the positives out of it, without doubt and don't let this particular match, this particular hour of tennis deter us from what we're trying to do."

Karolina Muchova completed a stunning comeback to upset world number one Ash Barty 1-6 6-3 6-2 in the Australian Open quarter-finals. 

Leading by a set and 2-0 in the second, Barty looked on track to reach back-to-back semi-finals at Melbourne Park, where she was bidding to become the first Australian woman to advance to the final since 1980 and first to lift the trophy since 1978.

But Czech 25th seed Muchova spoiled the 'Barty party' on Rod Laver Arena as her star opponent – unable to stop the rot – sensationally crashed out on Wednesday.

Muchova, whose only previous win against a top-five player came against Karolina Pliskova at Wimbledon two years ago, will contest her maiden major semi-final as either Jennifer Brady or Jessica Pegula await.

Played behind closed doors on the final day of a five-day state-wide lockdown in Victoria, Barty initially showed no mercy in warm and sunny conditions midweek.

Barty, who had lost the second-fewest games (20) en route to the last eight, raced out to a 5-0 lead in just 16 minutes – Muchova managing to avoid a first-set bagel in the only positive in an otherwise forgettable start.

Winner of the 2019 French Open, Barty only dropped three points on first serve, while she won 90 her cent of her second serves – finishing a lopsided first set with six winners and just as many unforced errors.

Progression to the semis appeared to be a foregone conclusion as Barty led and Muchova required a medical timeout away from the court at the end of the third game of the second set.

But Muchova emerged a new player, with Barty fading dramatically after everything she touched had turned to gold in the opening set.

Barty's unforced error count ballooned out to 19 as Muchova enjoyed great success on second serve, winning 12 of 15 points, while the former – who did not face a break point in the first set – only managed four of 15 and served three double faults.

Muchova continued her red-hot form in the deciding set - breaking in the opening game before saving a pair of break points to consolidate and she did not look back as she caused a boilover, which was sealed with an ace.

Data Slam: ​Barty loses her way
Unstoppable in a 24-minute first set, Barty crashed back down to earth thereafter. She missed routine shots consistently, with 31 unforced errors in the remaining two sets contributing to her demise.

WINNERS/UNFORCED ERRORS
Barty – 21/37
Muchova – 17/33

ACES/DOUBLE FAULTS
Barty – 3/3
Muchova – 2/3

BREAK POINTS WON
Barty – 3/13
Muchova – 4/11

Australian Open fans are set to return to Melbourne Park from Thursday after the Victorian government confirmed the lifting of restrictions following a five-day lockdown amid the coronavirus pandemic.

While the number of supporters set to attend remains unknown, fans will be back in their seats for the beginning of the Australian Open semi-finals, with record-chasing Serena Williams set to face three-time grand slam champion Naomi Osaka in Melbourne.

Defending men's champion Novak Djokovic will play the tournament’s surprise package, Russian qualifier Aslan Karatsev - who is the first player to reach a semi-final on their grand slam debut.

Djokovic was on court when the lockdown came into effect last Friday, with the five-day "circuit-breaker" designed to control an outbreak of the UK coronavirus strain.

Part of the third round, the fourth round and quarter-finals of singles action were played behind closed doors after a series of outbreaks in Victoria.

The state has recorded 12 more active cases since the lockdown was implemented but, with none discovered in the past 24 hours, Victorian premier Daniel Andrews announced restrictions will be eased.

"I'm very, very pleased to announce that the restrictions will come off, almost all of them, at midnight tonight," Andrews told reporters on Wednesday.

"From 11:59pm [Wednesday local time], the restrictions will be dropped [but] masks will be required indoors and outdoors when you can't socially distance."

The stage-four restrictions meant residents could not leave their homes for any other reason than work, shopping for groceries, exercise or the giving or receiving of medial care.

This year's delayed Australian Open has had crowds capped at 30,000 per day with original COVID-19 restrictions, but new limits are yet to be determined for the rest of the tournament.

"There will be meetings this afternoon [to determine] what is a safe number," Andrews said.

"They already were reduced, they may have to be reduced further, but that matter will be resolved in the next few hours."

Serena Williams admitted it felt like stepping back in time as her movement and power came together to overwhelm Simona Halep at the Australian Open.

It had been just over 18 months since Halep destroyed Williams in the Wimbledon final, and with the American great approaching her 40th birthday, prospects of a 24th grand slam title have appeared to fade.

Into the conversation on Tuesday strolled a revitalised Williams, a woman who has been proving a point and defying expectation for coming up to a quarter of a century.

Williams is simply not having it that her days as a winner might be over, which is why she and coach Patrick Mouratoglou are always seeking marginal gains.

Dogged by an Achilles injury since the US Open last September, Williams feels over that, and a 6-3 6-3 quarter-final win over Halep attested to that being the case.

More than that, though, Williams noticed the years fall away as she dashed around the court, thumping groundstrokes with abundant power and often plenty of precision.

Speaking of the movement returning, Williams said: "It was something that Patrick and I did discuss. I just wasn't able to incorporate it as much as I would have liked to.

"But once I was able to get on the court, I was able to incorporate it as much as I could. Movement has always been one of my strengths, and so it's actually more natural for me to move than for me not. So it was just kind of, like, 'Oh, that's how I used to move', so it's pretty good.

"I'm happy that I'm doing that again and that I put it back into my game. I think I was more focused on other things and not focused on something that is actually a strength of mine, has always been a strength of mine, and I had to refocus on that."

She faces Naomi Osaka next for a place in the final. It reads like a match-up of an all-time great against a player who could over time join her in that pantheon.

Osaka is pursuing a fourth grand slam title, while Williams wants the 24th as much as she craved the first, given it would move her alongside Margaret Court at the top of the all-time list.

The veteran American's most recent slam title came while pregnant in Australia four years ago, with Williams dealt four final defeats since, including a notable one to Osaka at the 2018 US Open.

If Osaka was watching Williams on Tuesday, as she surely was, the Japanese player could have only been impressed.

When asked about how she was matching and often out-matching Halep even in the longest rallies, Williams paused to consider when she was last able to boss such exchanges.

"It's definitely been a minute. It's been a long minute," she said with a smile. "I think 19... 1926, the summer of 1926 I think was the last time I felt that.

"But I'm good at rallying and I have to embrace the things I'm good at. I'm good at playing power, I'm good at hitting a hundred balls.

"That's one thing that's unique about me that I just need to kind of accept and embrace and just be good at both."

Williams and Osaka may have a crowd on Thursday for the semi-final, or they may not. Melbourne remains in lockdown but spectators could be back on Rod Laver Arena for the clash of two of the sport's biggest personalities.

Addressing that prospect, Williams indicated she would have mixed emotions.

"I love having the people there, obviously. But at the same time, it's kind of nice to not have, like ... more pressure when there is people in the stands," Williams said.

"So I think either way it's really a win-win situation. That's kind of how I look at it."

Fast-footed on the court, quick to sidestep off it, Williams is convinced she can push Osaka hard, perhaps heartened by a narrow win when they met in an exhibition match in Adelaide last month.

"I've got to keep going. Obviously I have an incredible opponent to play, so it would be nice to hopefully keep raising the level of my game. I'm going to have to," Williams said.

Halep said Williams "was stronger in the important moments", and she too noticed her opponent showing something near vintage form.

"Yeah, she's moving better and she hits strong," Halep added. "I feel like she's in a good shape now. She has a really good game. Always did..."

Former world number one Naomi Osaka is unfazed about her record at grand slams as she eyes consistency after reaching the Australian Open semi-finals.

Osaka will face either 23-time slam champion Serena Williams or Simona Halep in the semis following Tuesday's emphatic 6-2 6-2 win over Hsieh Su-wei in Melbourne.

Three-time major winner Osaka has gone on to win the title each time she has reached the quarter-finals of a slam – beating Hsieh en route to her 2019 Australian Open triumph.

Asked about the record, Osaka told reporters: "I don't really care about the stat. Just because I've only been to four quarter-finals.

"It feels something like 20. That would be cool. But four, it's not really doing too much for me.

"I would be more impressed if I didn't lose in finals. If it says 10-0 in finals. But the fact is if I don't reach the finals, I lose in the fourth round or the third round.

"For me, I'm happy to be more consistent. I think I'm being more consistent since New York, so that's the ultimate goal for me."

Osaka – in the midst of a 19-match winning streak – overpowered veteran Hsieh on Rod Laver Arena, where the Japanese star hit 24 winners and just 14 unforced errors, while she lost just two of her 25 first-service points.

It does not get any easier for Osaka, with record-chasing Williams or two-time slam champion Halep standing in the way of a trip to Saturday's decider at Melbourne Park.

"I played both of them before I think multiple times," Osaka – confident after saving two match points against Garbine Muguruza in the last 16 – said.

"Halep, I don't really like playing her. She's someone that's really tough, someone that gets the ball back every time. For me it's definitely a mental and physical battle.

"Of course, the same goes for Serena. She's Serena, someone that I feel really intimidated when I see her on the other side of the court."

Former world number one Naomi Osaka was relentless as she dismantled Hsieh Su-wei to reach the Australian Open semi-finals 6-2 6-2.

Hsieh upstaged the likes of 2019 US Open champion Bianca Andreescu en route to the quarter-finals, but the veteran was overpowered by Japanese star Osaka in Melbourne on Tuesday.

Three-time grand slam champion Osaka dominated from the outset, especially on serve – losing just two points on her first serve, as the third seed awaits record-chasing Serena Williams or Simona Halep in the final four at Melbourne Park.

Osaka emerged from the jaws of defeat in the last 16, saving a pair of match points to claim an improbable victory against last year's runner-up Garbine Muguruza.

And Osaka was a woman on a mission in sunny and warm conditions on Rod Laver Arena, where the 23-year-old broke for an early 3-1 lead.

Hsieh – the oldest player in the Open Era to make her grand slam quarter-final debut, aged 35 – had the chance to break back immediately, but Osaka held firm after fending off a pair to consolidate.

Osaka, who has gone on to win the title each time she has reached the quarter-finals of a major – beating Hsieh en route to the 2019 Australian Open crown, had another two break points saved but she still cruised in the first set.

It was a powerful but disciplined performance from Osaka, particularly on serve as she won 100 per cent of her points on first serve (12 of 12) against a helpless Hsieh.

The second set followed a similar theme – Osaka maintaining her dominance as she raced out to a 3-0 lead.

Osaka never relinquished the break, closing out the match on Hsieh's serve, with the six-time WTA Tour champion improving to 4-0 in quarter-final matches at slams, and 2-0 at the Australian Open.

Data Slam: ​Osaka extends streak
Eyeing a second Australian Open trophy, Osaka has now won 19 consecutive matches, dating back to February last year following the Tour's resumption amid the coronavirus pandemic. She last lost while on Fed Cup duty with Japan.

WINNERS/UNFORCED ERRORS
Osaka – 24/14
Hsieh – 14/23

ACES/DOUBLE FAULTS
Osaka – 7/1
Hsieh – 0/3

BREAK POINTS WON
Osaka – 4/12
Hsieh – 0/3

A third consecutive Australian Open quarter-final beckons for Ash Barty but the world number one is far from satisfied as she eyes a drought-ending title in Melbourne.

Barty produced a masterclass to blitz American Shelby Rogers 6-3 6-4 in the fourth round on Monday.

Not since Wendy Turnbull in 1984 has an Australian woman reached three successive quarter-finals or more at Melbourne Park, where Barty will meet Karolina Muchova in the last eight.

But 2019 French Open champion Barty is dreaming big as she looks to become the first Australian woman since 1978 to take the title.

"We're not done yet," Barty,a semi-finalist last year, said. "Obviously it's exciting to be in another quarter-final of a grand slam, particularly here in Australia.

"If we had looked at the way we were preparing during our pre-season, to have the start that we have had so far is really encouraging, but certainly not satisfied with where we're at at the moment. 

"We will keep chipping away and keep trying to do the right things to progress as far as we can."

Barty arrived in Melbourne at the start of the year having not played in a competitive WTA Tour event since February 2020 due to the coronavirus pandemic.

Asked about the prolonged break, Barty – who stepped away from tennis in 2014 before returning in 2016 after playing cricket – said: "I think I know that I've done the work. I know that we prepared in the right way during the pre-season. 

"We've done all the work to try to give myself the opportunity to play a good level of tennis and to a level that I know I'm capable of. It's just knowing that I put the trust in the work that we've done, more than surprising myself.

"I think I've known that I've done the work. I have the ability to play at this level and then it's just about going about all of our processes, our routines the right way. All of those came back quite naturally.

"It's something that I've practiced a lot, and I gain my confidence from that practice and from those preseasons as opposed to just match results."

Jessica Pegula said she "can't be more confident" after upsetting Elina Svitolina to reach her first grand slam quarter-final and Ash Barty stayed in the hunt for Australian Open glory on Monday.

Pegula, the daughter of NFL and NHL franchise owners of the Buffalo Bills and the Sabres, beat fifth seed Svitolina 6-3 3-6 6-3 on Rod Laver Arena to set up a showdown with her fellow American and friend Jennifer Brady.

Brady made it all the way to the semi-finals of the US Open last year and has now put together her best run at Melbourne Park after seeing off Donna Vekic 6-1 7-5.

World number one Barty has not dropped a set in her home major and started the second week by dispatching Shelby Rogers 6-3 6-4.

The top seed from Queensland's next assignment will be a meeting with Karolina Muchova, who saw the back of Elise Mertens 7-6 (7-5) 7-5.

Muchova, the 25th seed from the Czech Republic, has made it through to her second grand slam quarter-final - having also reached this stage at Wimbledon in 2019 - without losing a set.

Pegula to put friendship to one side

Pegula and Brady are close friends, but they will have to put that to one side when they meet in the quarter-finals.

The world number 61 claimed her first victory over an opponent ranked in the top 10 just over a month after Svitolina beat her in straight sets in Abu Dhabi.

Pegula hit 31 winners to Svitolina's 19 and won 21 points from 29 when she made a trip to the net as she broke new ground at a major

She said: "I can't get more confident, it's my best result yet and I'm playing good tennis. Today was a hard-fought win, so, yeah, feeling pretty good."

Pegula added on the prospect of facing Brady: "We're here to have fun and compete. If I can do it against somebody that I like, that I wouldn't mind if they beat me, hopefully not, but if they did, why not?"

Brady benefited from strict lockdown

Many players understandably struggled during and after being in a strict two-week lockdown in a hotel room following their arrival in Australia.

Brady was among the players who were not allowed out of their rooms for a fortnight, but said she used the situation to recharge her batteries before the first major of the year.

The 22nd-seeded Pennsylvanian said: "I think it was a little bit of a benefit for me, just taking a break from tennis. I had been going non-stop since World Team Tennis in June. I didn't take any time off.

"I was playing from June and then played US Open, the U.S. tournaments, and then went straight to Europe, then finished there and was training in Europe, then went home for Christmas and then came and started in Abu Dhabi.

"So obviously I didn't really feel super fresh mentally coming into Abu Dhabi. And then when I was away from tennis for two weeks, I felt like I wanted to play again to compete and I think that helped me."

Much improved Czech

Muchova had not been beyond the second round of the Australian Open before last week but now has a semi-final spot in her sights.

The 24-year-old was 4-0 down in the opening set as Mertens got off to a flyer but warmed to the task with her battling spirit and positive approach.

Muchova converted five of the six break points she earned on Margaret Court Arena, also coming from a mini-break down in a first-set tie-break.

She struck 25 winners to Mertens' 15 and advanced despite making 31 unforced errors, getting her rewards for throwing caution to the wind.

World number one Ash Barty secured another quarter-final berth at the Australian Open after outclassing Shelby Rogers 6-3 6-4.

It was a Barty party on Rod Laver Arena, where the 2019 French Open champion dominated from the outset to see off unseeded American Rogers in a little over an hour on Monday.

Barty, who appeared in the semi-finals in Melbourne last year to become the first Australian woman to reach that stage since Wendy Turnbull in 1984, raced past Rogers to set up a meeting with Karolina Muchova.

Home hope Barty and Rogers renewed acquaintances behind closed doors in the last 16 after the former won a match tie-break against last year's US Open quarter-finalist en route to claiming the Yarra Valley Classic.

Barty was unstoppable from the start, striking first in the fourth game and breaking for a 3-1 lead after precision play left Rogers helplessly scrambling around the court.

There was a test for Barty after Rogers earned a pair of break points in the seventh game, but the former saved both.

It was the only real challenge in a first set controlled by Barty, who continued where she left off in the second.

While Rogers showed glimpses, Barty – moving freely with all eyes on her heavily strapped thigh – was firmly in the groove as she broke for a 2-1 lead.

Another break followed but there was a blip for Barty, who was broken for the first time when serving for the match at 5-2 in a late Rogers resistance which only delayed the inevitable.

Data Slam: ​Three in a row for Barty
Barty will contest her third consecutive Australian Open quarter-final. Not since Wendy Turnbull in 1984 has an Australian woman enjoyed such a run. Barty is bidding to become the first Australian woman to win the grand slam since 1978.

WINNERS/UNFORCED ERRORS
Barty – 21/16
Rogers – 14/25

ACES/DOUBLE FAULTS
Barty – 5/3
Rogers – 5/1

BREAK POINTS WON
Barty – 3/6
Rogers – 1/3

Serena Williams is moving better than she has in years, according to her coach Patrick Mouratoglou.

Williams, 39, has looked in good form at the Australian Open as she eyes a record-equalling 24th grand slam singles title.

The American has dropped just one set on her way to the quarter-finals, in which she faces Simona Halep on Tuesday.

Mouratoglou said Williams' movement was the best it has been in several years.

"First of all, it's something that we have put the emphasis on because in tennis that's probably one of the most important things. If you are late on the ball, you can't do what you want to do. Sometimes you don't even touch the ball," he told a news conference on Monday.

"It's a sport where you have to be able to move fast from side to side and long enough. It's something that probably in the last two, three years, this had consequences for Serena.

"Even more, when you're not in a good day, you need a plan B. To be able to have a plan B, you have to be able to move well. If you can't move well, there is no plan B. The only plan is attack.

"I think it cost her a few important matches. So we have decided to find a way to bring back the footwork that she used to have in the past. I feel like she's done a great job. She's moving much better."

Williams last won a major title in Melbourne in 2017, losing four grand slam finals since then.

With all eyes on her as she aims to equal Margaret Court's record of 24 grand slam singles titles, Mouratoglou insisted that mark was not an obsession for Williams.

"Does she need that validation? I don't think she needs that validation.  But, I mean, clearly she came back to tennis to win some other grand slams, so that's for sure the goal," he said.

"Now, she's not as obsessed with the 24 than most of the people in the tennis world, but definitely she wants to win grand slams. That's the only reason why she came back to tennis."

Simona Halep set up a quarter-final duel with Serena Williams after showing admirable character to battle back from a set down to beat Iga Swiatek 3-6 6-1 6-4 and seal her 100th grand slam match win.

Halep and Swiatek put on a thrilling show in the night session on Sunday, as the Romanian two-time grand slam champion demonstrated her fighting spirit to come from a set down and reach the last eight.

Swiatek took charge in the first set after saving the first two break points of the contest, eventually putting herself in a commanding position as she won the 10 of the final 11 points of the set, but Halep remained focused as her 19-year-old opponent began to wobble in the second.

Halep then snuffed out any threat of a turnaround by breaking back straight after losing on her own service in the decider and she went on to set up a meeting with Williams, who had overpowered Aryna Sabalenka earlier in the day.

Naomi Osaka also advanced, though she was by no means comfortable, while Hsieh Su-wei beat Marketa Vondrousova in straight sets.

HALEP'S REVENGE

Halep's clash with Swiatek was their first since the French Open last October, when Swiatek ran out a 6-1 6-2 winner and went on to claim her maiden major title.

Revenge was on the cards at Melbourne Park and Halep got the job done impressively, showing her mettle to return from a set down.

"Well, I thought before the match that I have to be a little bit more aggressive than Paris. In Paris I have been very far back, and my ball didn't go through the court," the second seed said. "So, I thought that it's a better chance to go and hit.

"The pressure came from the way I played the last match against her. I just expected a better game from myself, which I did, and I'm really happy about that."

Halep accepts facing Williams will be an entirely different challenge, but she remains confident despite lauding the American a "legend" in her on-court interview.

"Of course it's different, she's the only one with 23 grand slams, so you cannot compare Serena with all of us, because we do not have so many grand slams," Halep added.

"But when I step on the court, it's just another opponent, and always I'm focused on myself more than I focus on who I play. We played so many times. I know what to expect. I will just try to do my game, and I will be confident."

WILLIAMS ON COURSE

All eyes are on Williams yet again, as she hopes to equal Margaret Court's record of 24 grand slam titles – and on the evidence of her latest win, she will take some stopping as she won 6-4 2-6 6-4.

Williams revealed she had to cope with a little off-court stress this week with her clothing line, and Sabalenka certainly kept the pressure up as the 22-year-old took the second set.

But Williams responded well to the seventh seed, who became the first player to take a set off the former world number one. Williams said she remained confident despite that setback.

"Like I said on the court, I just felt like even games that I lost, I was so close to winning. Not all games, but probably most of those games," she said. "I just needed to play better on the big points.  I knew that I could. I still hadn't reached my peak. I was like, 'Okay, Serena, you got this, just keep going.'"

OSAKA RELEASES HER ANGER

Osaka was in a real spot of bother against Garbine Muguruza, but saved two match points.

The 2019 champion Osaka steadied herself and felt more composed after a brief show of frustration, as she struck the ground with her racquet.

Ultimately, she emerged a 4-6 6-4 7-5 victor, and Osaka felt letting frustration get the better of her for a moment helped her cause.

"On the first match point, I was just thinking that I didn't hit a decent serve that entire game, so I should really focus on my serve," he said. "I feel like my serve stats were pretty good that set, so I was just telling myself to do better.

"Then on the second point, when the rally started, I just told myself not to push [the ball] but also don't do something crazy and make a really bad unforced error. I felt the entire match I was overthinking. There was a moment when I got angry and hit my racquet on the ground. I feel like I released a lot of the thoughts that I had. It just made me go more into instinct-based tennis."

She will face Hsieh next, the world number 71 having beaten Vondrousova – ranked 51 places higher – 6-4 6-2.

Serena Williams calmed injured fears after coming through a thrilling back-and-forth against Arnya Sabalenka to reach the quarter-finals of the Australian Open.

Williams, who is pursuing a record-equalling 24th career grand slam and her first major victory in four years, prevailed 6-4 2-6 6-4 after more than two hours on court against seventh seed Sabalenka.

Her struggles during the second set appeared partly attributable to a fall but Williams recovered her poise and the 39-year-old does not expect any ill-effects in a last-eight showdown against either Simona Halep or Iga Swiatek.

"I don't think so. It didn't hurt at all. I didn't roll my ankle, so that was good," she told reporters.

"Yeah, I think it was just dramatic, me being dramatic.

"My first thought was, 'Not another ankle sprain in Australia'. But I knew immediately that it wasn't.

"Then I was more embarrassed than anything. I was like, 'Oh, my goodness'."

Williams moved well throughout the contest, assuaging any lingering concerns over Achilles problems that have dogged her of late - even manging to rally when Sabalenka reeled off three consecutive games from 1-4 down in the decider.

"I've worked really hard on my movement. Yeah, I like retrieving balls. I mean, obviously I like to be on the offense, but I can play defence really well, as well.

"I do get a lot of balls back when I need to. I didn't think about my Achilles. It's so good to not think about it. Oh, my goodness. It's been a problem actually since 2018.

"I just never want that problem again. It feels really good to just play and to run, to not feel that. It's a great relief."

Arguably Williams' greatest inconvenience around the match was not a physical one, after she had to participate in a Saturday conference call to avert an "emergency" at her clothing business.

"Tennis is a lot less stressful. I don't have to manage a team. I do manage a team actually, but it's different," she chuckled. "Even though I am the CEO of my tennis team, it's definitely different.

"I think a part of me loves being on the court because it's free-flowing. It's not like I have to kind of just manage and make sure everyone is able to perform.

"I have a second career and it's fun. One of our main players, our employees, had an emergency. You got to step it up when you got to step it up.

"I was smart about that. I scheduled a call directly after my practice. I was like, 'Okay, I can do it early and still have the rest of the day to relax'.

"And it was during [Williams' daughter] Olympia's nap, so it was perfect."

Serena Williams moved a step closer to a record-equalling 24th grand slam title after outlasting Aryna Sabalenka in an absorbing battle to reach the Australian Open quarter-finals.

Williams – in pursuit of Margaret Court's record slam haul of 24 – has not tasted major success since winning the Australian Open in 2017.

But former world number one Williams and her bid to match Court remains on track following Sunday's thrilling 6-4 2-6 6-4 victory over seventh seed Sabalenka after more than two hours.

No fans were allowed to attend Melbourne Park amid a coronavirus lockdown in Victoria, but there was still plenty of noise inside Rod Laver Arena in a battle between two big hitters.

Williams, who reached 90 Australian Open wins in 101 appearances in Melbourne last time out – she has played and won more matches than any other woman in the tournament's history, prevailed in a tense opening set.

After fending off a break point in the seventh game, Williams – moving extremely well against the 22-year-old – was gifted a second break-point chance of her own three games later and she pounced as Sabalenka fired a forehand into the net.

The seven-time Australian Open champion hit 12 winners and just nine unforced errors in a fast and ferocious first set.

Williams owned a career 53-8 record in last-16 matches at grand slams heading into the contest – last falling at this stage when she pulled out ahead of her French Open showdown with Maria Sharapova in 2018, while her last match loss at this stage came in Melbourne in 2014.

But Sabalenka was unperturbed, the Belarusian – eyeing her maiden slam quarter-final – an unstoppable force against a helpless Williams in the second set, breaking in the first, third and fifth game.

Williams, who only made 36 per cent of her first serves, was moved around the court as she dropped a set for the first time at this year's Australian Open.

Having cut a frustrated figure in the second set, Williams emerged with renewed figure in the decider – the 39-year-old claiming the decisive break of serve in the fourth game for a 3-1 lead before digging deep to consolidate.

Sabalenka reeled off three consecutive games to put the match back on serve, but she was unable to maintain her charge against Williams, who closed out the match on her opponents' serve.

Data Slam: Serena steps up on serve
Not much went right for Williams on serve in a lopsided second set. But when it mattered most, the 12th seed stepped up by serving at 71 per cent in the third – winning 17 of 22 first-serve points against Sabalenka.

WINNERS/UNFORCED ERRORS
Williams – 30/26
Sabalenka – 24/36

ACES/DOUBLE FAULTS
Williams – 9/8
Sabalenka – 4/4

BREAK POINTS WON
Williams – 4/9
Sabalenka – 4/11

Former Australian Open champion Naomi Osaka saved a pair of match points as she emerged from the jaws of defeat to sensationally prevail against Garbine Muguruza en route to the quarter-finals.

Osaka moved through to the last eight in Melbourne for the second time in three years after the Japanese star and former world number one rallied past two-time grand slam champion Muguruza 4-6 6-4 7-5 on Sunday.

Muguruza – last year's runner-up at Melbourne Park – led 5-3 and was up 40-15 on Osaka's serve in the final set before the latter reeled off four successive games to complete a great escape on Rod Laver Arena.

Winner of the Australian Open in 2019, third seed Osaka had been down 6-4 2-0 earlier in the match when she mounted an improbable fightback against the Spanish star.

It was a milestone moment for Osaka as the three-time major champion celebrated her 50th grand slam victory and extended her winning streak to 18 matches, dating back to February last year after the coronavirus pandemic halted the WTA Tour season in 2020.

Osaka, who hit 40 winners and 11 aces against Muguruza, has gone on to win the title each time after advancing past the last 16 of a slam – US Open in 2018 and 2020 and 2019 Australian Open.

Next up for Osaka is Taiwanese veteran Hsieh Su-wei for a spot in the semi-finals.

Australian Open tournament director Craig Tiley said the grand slam will "continue as normal" after Greek tennis player Michail Pervolarakis tested positive for coronavirus following his departure from Australia.

The delayed Australian Open, already being played amid strict COVID-19 measures in Melbourne, has been forced to go behind closed doors without fans due to a five-day state-wide lockdown in Victoria.

As Victoria stays locked down until Wednesday, Pervolarakis revealed via social media that he tested positive for COVID-19 upon his arrival in South Africa.

Pervolarakis did not feature in the Australian Open but did team up with fifth seed Stefanos Tsitsipas for Greece in the ATP Cup at Melbourne Park prior to the year's opening slam.

Tiley addressed the situation on Sunday and told Channel Nine's The Today Show: "After spending a day in South Africa [he] tested positive.

"While there's a link in the fact he left here, it is going to be up to the advice of the health authorities.

"The good news for us is he tested negative and then left … there's a fair bit of travel time [in between].

"It was a week ago we got everyone tested again, everyone tested negative."

Tiley added: "No again we will continue on [as] normal.

"Obviously anyone on sight that has any symptoms related to COVID is required to immediately isolate and test, we haven't had any of that."