Ash Barty has won the WTA's Player of the Year award for a second time, while Emma Raducanu's sensational 2021 season was capped with the Newcomer of the Year prize on Tuesday.

Barty collected the tour's top individual year-end award in 2019, having won the French Open and finished that season as the world number one.

And after Sofia Kenin succeeded her in 2020, Barty is back on top this year.

This was the third straight season the Australian superstar claimed the year-end number one ranking, and it saw her land a second major title at Wimbledon. Barty's five WTA titles in 2021 were unsurpassed.

But she has had to share the limelight in recent months with Raducanu, and that was the case again as the 19-year-old Briton was unsurprisingly hailed as the tour's star newcomer.

Raducanu became the first qualifier to win a grand slam when she swept to glory at the US Open, having also impressed in a run to the last 16 at Wimbledon.

The teenager, who has risen from 343rd to 19th in the rankings in the past year, won 10 straight matches without dropping a set from the first qualifying round to the final at Flushing Meadows.

Elsewhere, Roland Garros champion Barbora Krejcikova collected a pair of awards, scooping Most Improved Player and, alongside Olympic, WTA Finals and French Open-winning partner Katerina Siniakova, the Doubles Team of the Year.

Carla Suarez Navarro, who retired in 2020 and was then diagnosed with Hodgkin's Lymphoma, returned to the tour cancer free in 2021 for a farewell season and carried off the Comeback Player of the Year award.

Karolina Pliskova stayed in the hunt for a place in the last four of the WTA Finals with a 0-6 6-4 6-4 victory over Barbora Krejcikova, though her hopes hinged on Anett Kontaveit defeating Garbine Muguruza later in the day.

World number three Krejcikova did not have a win to her name in Mexico, losing to Kontaveit and Muguruza, but raced into the ascendancy on Sunday as she claimed the first set in just 26 minutes of an all-Czech tussle.

Pliskova, who had won both prior singles meetings between the pair, responded brightly in the second set before Krejcikova broke her fellow Czech's serve to take a 3-2 lead and seemingly edge closer to victory.

However, world number four Pliskova fought back by breaking in consecutive Krejcikova service games to level the match. The contest then teetered in the balance in the decisive set but, despite producing a double fault in the penultimate game, Pliskova downed Krejcikova to maintain hopes of an appearance in the final four in Guadalajara.

Wimbledon runner-up Pliskova won earlier in this tournament against Muguruza, who was set to face Kontaveit later on Sunday.

The 29-year-old Pliskova was sure to be paying close attention to that match. She needed Kontaveit, already through to the last four, to beat Muguruza and that would be enough to confirm the Czech's place in Group Teotihuacan's top two.

However, a win for Muguruza would see the Spanish sixth seed go through alongside Kontaveit, with Pliskova eliminated.

WINNERS/UNFORCED ERRORS 

Pliskova – 10/30
Krejcikova – 21/21

ACES/DOUBLE FAULTS 

Pliskova – 11/12
Krejcikova – 4/8

BREAK POINTS WON 

Pliskova – 3/8
Krejcikova – 4/11

The 2021 WTA Finals look set to be a fitting end to a fascinating season on the Tour.

The 50th year-ending championships, which will take place in Guadalajara instead of Shenzhen due to coronavirus restrictions, will see eight of the top-10 ranked players come together in two round-robin groups, with four semi-final places up for grabs.

Six of the eight competitors will make their debuts at the event, while only two grand slam finalists from this year – and just one champion – will be present. With world number one Ash Barty withdrawing because of concerns around possible quarantine issues, it really does feel like an open draw.

Stats Perform looks at the eight Finalists and the key data you need to know before the action gets underway...

Group Chichen Itza

Aryna Sabalenka (1)

World number two Sabalenka is the top-ranked competitor in Guadalajara, with 44 match wins this year and titles in Abu Dhabi and Madrid, where she beat Barty.

The Belarusian boasts formidable weapons: Sabalenka has won 71.1 per cent of first-serve points and has an average of 8.4 forehand winners per match on the Tour this season, both of which are best figures among the eight Finalists.

She has only played two matches since losing to Leylah Fernandez in the US Open semi-finals, though, both of which were at last month's Kremlin Cup in Moscow.

Did you know? Since the start of 2018, Sabalenka has won the joint-most matches (three) in WTA Tour main draws after losing the first set 0-6. At the same time, she is 9-13 in three-set contests in 2021.

Maria Sakkari (4)

The nearly-woman of 2021, Sakkari has reached more semi-finals this year (seven) than anyone else on the WTA Tour, including at two of the four slams, but made it to just one final (in Ostrava, where she lost to Anett Kontaveit).

Still, this has been a historic year for the 26-year-old, who became the first Greek woman to reach a major semi-final, enter the top 10 and qualify for the season-ending championship.

Since the start of the US Open, Sakkari has lost only four of 14 matches, a run that includes the semi-final of the Kremlin Cup where she retired due to dizziness.

Did you know? Nobody has won more Tour-level matches against top-10 opponents this year than Sakkari (seven, level with Barty and Jessica Pegula). Before 2021, her record in such matches was 10-13.

Iga Swiatek (5)

Swiatek, the 2020 French Open champion, is the youngest competitor at these Finals at 20 years and 170 days old (as of the tournament's end). She is just the second player born this century to reach this event, after Bianca Andreescu in 2019.

Although unable to get beyond the quarter-finals of a major this year, Swiatek did win titles in Adelaide and Rome, where she inflicted a double bagel on Karolina Pliskova in the final.

Her success in Australia was her first on a hard court, a surface on which she won 19 of 28 matches this year.

Did you know? Swiatek has won 58 per cent (28 of 48) of her matches this season in straight sets, the highest ratio among the Finalists.

Paula Badosa (7)

A successful year for Badosa has been built on clay: she won a Tour-leading 17 matches on the dirt in 2021, reaching the French Open quarter-finals, the last four in Madrid and Charleston and winning the title in Belgrade.

This has been a breakthrough season for the 23-year-old across all surfaces, though, one that culminated in a record-breaking three-set win over Victoria Azarenka in the final at Indian Wells last month.

Badosa clinched that match after a third-set tie-break. She has won four deciding sets in that fashion this year, the most of anyone on the WTA Tour.

Did you know? Badosa has won seven matches (excluding the Olympics) after dropping the first set in 2021. Nobody else has as many come-from-behind victories among the Finalists.

Group Teotihuacan

Barbora Krejcikova (2)

The only major singles champion from 2021 at these Finals, Krejcikova has enjoyed a remarkable rise this year.

Along with success at Roland Garros, where she also triumphed in the doubles, the Czech won titles in Strasbourg and Prague; only world number one Barty (five) and Kontaveit (four) have won more this year.

Among the eight finalists, Krejcikova boasts the highest break-point conversion ratio (49.7 per cent, or 142/286) and break-point saved figure (66.4 per cent, or 150/226) for this season. She has become a clutch competitor and will be hard to stop in Mexico, both in the singles and the doubles.

Did you know? Krejcikova has won six matches against top-20 opponents in her career. All six of those wins were in 2021.

Karolina Pliskova (3)

Pliskova boasts impressive experience of the year-ending event: she is only the fourth player to qualify for five or more WTA Finals since the current format was introduced in 2003 (after Agnieszka Radwanska, Petra Kvitova and Azarenka).

Beaten in her three Tour finals this year, including Wimbledon, the 29-year-old will be desperate to go at least one better than her three consecutive semi-final appearances at this event.

Pliskova begins against Garbine Muguruza, a player she has beaten twice before at the season-ending tournament.

Did you know? Pliskova leads the Tour for aces this season with 364, hitting a year-best 21 in her round-of-16 match with Jelena Ostapenko in Stuttgart. It's the fourth time in the past six seasons Pliskova has been top of the aces standings.

Garbine Muguruza (6)

This is the first time since 2000 that two Spanish players have contested the Finals. Back then, it was Conchita Martinez and Arantxa Sanchez Vicario at Madison Square Garden in New York.

Muguruza, champion in Dubai and Chicago this year, has won more matches on hard courts (34) than anyone else in 2021 aside from Kontaveit. She also boasts the best average for successful net approaches this year (3.0) among the Finalists, which will make her a challenging obstacle in what will be her first Finals since 2017.

The former world number won made a career-high four Tour finals this year and won more than one trophy in a season for just the second time, sending her back into the top 10 for the first time since 2018. 

Did you know? Muguruza boasts a 10-1 record in WTA tournaments in Mexico, winning back-to-back titles in Monterrey in 2018 and 2019.

Anett Kontaveit (8)

With a Tour-leading 37 hard-court wins this year and on a formidable run of form, Kontaveit could spring a surprise at her first Finals.

After losing her fifth match in a row to Ons Jabeur on August 17, the Estonian went on a run of 26 wins from 28 matches, lifted four titles and broke into the top 10 for the first time. It was Jabeur she edged out for a place at this tournament after she won her fourth title of the year at Cluj-Napoca.

Along with Barty, Kontaveit is the only player to reach six Tour-level finals this year, while nobody at the season-ending tournament has won more titles (four).

Did you know? Kontaveit has hit the most backhand winners (293) on hard courts on the WTA Tour in 2021, averaging nearly six per match.

Australia and Switzerland secured their spots in the semi-finals of the Billie Jean King Cup and will go up against each other for a place in the final.

Belarus proved no match for Australia, who got the job done across their two singles matches on the day in the Czech Republic.

Storm Sanders got the ball rolling as she comfortably saw off Yuliya Hatouka 6-3 6-3 in the first contest of the day in Group B.

Ajla Tomljanovic was made to work a little harder by Aliaksandra Sasnovich as she lost the first set but eventually rallied to overcome her opponent 4-6 6-2 6-3.

It meant the two countries' doubles meeting was a dead rubber – Belarus at least took the opportunity to avoid a 3-0 annihilation as Sasnovich teamed up with Lidziya Marozava in the 6-4 6-4 defeat of Olivia Gadecki and Ellen Perez.

In Group D, Switzerland and the Czech Republic claimed one victory apiece in the singles – Marketa Vondrousova had too much for Viktorija Golubic in a 6-4 6-2 success that gave the Czechs the upper hand.

But Belinda Bencic levelled things up despite the unenviable task of facing world number three Barbora Krejcikova, emerging with a 7-6 (7-2) 6-4 success.

Bencic was then involved in the doubles decider as well, getting the better of Lucie Hradecka and Katerina Siniakova with Jil Belen Teichmann, their 6-3 6-3 win sealing the semis spot for the Swiss.

The Russian Tennis Federation – who eliminated defending champions France on Wednesday – and the United States are due to contest the other semi-final.

Iga Swiatek was knocked out of the Indian Wells Open in the round of 16, the second seed headlining the list of casualties on Tuesday.

Swiatek was swept aside by Jelena Ostapenko in the battle between two previous French Open champions in the desert.

Elina Svitolina, reigning Roland Garros champion Barbora Krejcikova and US Open runner-up Leylah Fernandez were also sent packing from the WTA Premier 1000 event.

SWIATEK CRUMBLES

After top seed Karolina Pliskova was eliminated on Monday, 2020 French Open champion Swiatek crashed out following a 6-4 6-3 defeat to Ostapenko.

Ostapenko – the 2017 Roland Garros winner – rallied from a break down in each set to reach the quarter-finals at Indian Wells, where the 24th seed hit 25 winners to 21 unforced errors in 93 minutes.

"I knew it was going to be a very tough match because she's such a great player, she won a grand slam and she's playing great tennis," Ostapenko said.

Standing in the way of Ostapenko and the semi-finals is Shelby Rodgers, who edged Flushing Meadows finalist Fernandez 2-6 6-1 7-6 (7-4).

SVITOLINA UPSTAGED BY PEGULA

Svitolina's campaign in the desert did not go according to plan, the fourth seed crushed 6-1 6-1 by Jessica Pegula.

Pegula – the 2021 Australian Open quarter-finalist – dismantled Svitolina in just 68 minutes for her seventh last-eight appearance of the season and fourth at WTA 1000 level.

"I think I've just been making a lot of really good decisions in the right moments," said Pegula, who will face two-time grand slam champion Victoria Azarenka following her seventh top-10 victory. "That obviously comes with playing a lot of matches, winning and getting confidence... it's just been more belief that I can play at this level. I think this year, I realised that, and I've been having good results."

KERBER POWERS THROUGH AS KREJCIKOVA FALLS

Three-time major winner and 10th seed Kerber will feature in the quarter-finals after overpowering Ajla Tomljanovic 6-4 6-1.

Kerber will next meet 21st seed Paula Badosa, who shocked third seed and reigning French Open champion Krejcikova 6-1 7-5.

"I think I played a pretty good match today," Badosa said. "I knew I had to play on a high level against Barbora. She's an amazing player, very talented. We played before so I knew what I was going to find there on court. I'm feeling good and I'm very happy that I could play my best today."

Top seed Karolina Pliskova suffered a shock defeat while defending champion Bianca Andreescu and Coco Gauff also were on the wrong end of upsets Monday at the Indian Wells Open. 

World number 115 Beatriz Haddad Maia of Brazil stunned Pliskova in straight sets to reach the round of 16 at a WTA Premier 1000 event for the first time.

The 15th and 16th seeds, Gauff and Andreescu, also exited in two sets, albeit to seeded players. 

LUCKY LOSER OUSTS PLISKOVA 

Haddad Maia lost in the final round of qualifying but made the main draw as a lucky loser when Nadia Podoroska withdrew through injury, and she has made the most of that reprieve with a 6-3 7-5 defeat of the world number three. 

She had faced Pliskova once before and it did not go well, a 6-1 6-1 rout at the 2018 Australian Open, but the Czech struggled to find her trademark serve amid powerful winds in the California desert.

Pliskova suffered 12 double faults and won just 43.4 per cent of points on her serve, whole Haddad Maia saved nine of the 14 break points she faced on her own serve. 

KONTAVEIT STAYS HOT TO DETHRONE ANDREESCU

Haddad Maia next faces 18th seed Annett Kontaveit, who ousted Andreescu 7-6 (7-5) 6-3 to end the Canadian's dreams of a repeat. 

Kontaveit has won 15 of her last 16 matches, winning titles in Cleveland and Ostrava during that stretch. Monday, she captured the first set on her fifth set point before rallying from a 3-1 deficit in the second to run the table and seal the win.

"It was extremely close throughout the match and I was just trying to stay tough. I was ready for a tough match," Kontaveit said. "She's such a good player, such a great competitor, so I knew it wasn't going to be over until it was really over."

BADOSA BOUNCES GAUFF

Paula Badosa, the 21st seed, breezed past Gauff 6-2 6-2 as the American teen also had trouble with her serve, hitting just two aces after recording 12 in her previous match. 

In a meeting of the last two defeated finalists in the tournament, 10th seed Angelique Kerber beat 20th seed Daria Kasatkina 6-2 1-6 6-4. 

Third seed Barbora Krejcikova handled Amanda Anisimova with ease, 6-2 6-3. 

Ons Jabeur, the 12th seed, had little trouble in downing 22nd seed Danielle Collins 6-1 6-3. 

Aryna Sabalenka has ranked among the top dozen players in the world since 2018, but her grand slam results always seemed underwhelming. 

In 12 career majors heading into 2021, Sabalenka had advanced past the third round only once, a fourth-round exit at the 2018 US Open. 

Now she is into her second successive grand slam semi-final after defeating Barbora Krejcikova 6-1 6-4 Tuesday, and she said the adjustments she has made this year have paid off. 

"I think I improved my volley game, my slice game," Sabalenka told ESPN after her latest win. "I mean, I would like to say my service game [too] but today's didn't work well."

She added with a smile: "I don't know, maybe the court's a little bit smaller, I don't know, I need to check it. But, yeah, I improved a lot."

Indeed, Sabalenka won seven of eight net points (to eight of 14 for her opponent) and consistently won points on her first serve even though it did not go in as often as she would have liked. 

Sabalenka entered the match having won 82 per cent of points on her first serve in the tournament and was down to 76 per cent Tuesday as she got only 57 per cent of her first serves in the court, but that was plenty good enough to handle Krejcikova. 

She said she focussed on putting as many balls back in play as she could and believed that was the key to her victory, as her opponent had 29 unforced errors and just 14 winners. 

Though the match was rather one-sided, Sabalenka enjoyed the support of the crowd in her first time playing Arthur Ashe Stadium during the night session. 

"I really love to be in New York and the US Open, one of my favourite slams, and I'm really enjoying my game here and every second on this court," she said. 

She also knows she probably will not get the same level of fan support in the semi-final, where she will face Canadian teen sensation Leylah Fernandez. 

"She's playing well, she's moving well and the crowd here [is] for her so I would say it's like nothing to lose for her," Sabalenka said. "It's going to be interesting match and I'm really looking forward to this one."

Aryna Sabalenka is into the semi-finals at a second successive grand slam after making easy work of Barbora Krejcikova at the US Open on Tuesday. 

The second seed cruised past eighth-seeded Krejcikova 6-1 6-4 to set up a semi-final meeting with Canadian teen Leylah Fernandez at Flushing Meadows. 

Sabalenka is coming off a semi-final appearance at Wimbledon, her best career result in a major, and she was rarely tested in her quarter-final rout of Krejcikova.

The pair appeared evenly matched heading in, both having won 42 matches this year with Krejcikova taking three tournament titles – including Roland Garros – and Sabalenka two. But there was a clear separation between the pair on this night at Arthur Ashe Stadium. 

Sabalenka started strong, breaking Krejcikova in her first service game to take an early lead and never looking back as she hit 12 winners to the Czech's five in the opening set.

Krejcikova lost her last chance to salvage the first set in the sixth game, as she double-faulted on the fourth break point she faced in the game to give Sabalenka a 5-1 lead before the Belarusian had an easy hold to secure the set. 

The second set featured more of the same as Sabalenka broke her opponent in the opening game, dropping only one point as Krejcikova imploded with three unforced errors and a double fault. 

Sabalenka was not quite as sharp as the set unfolded, falling behind 0-30 in consecutive service games, but she fought back to win both without facing a break point. 

While Krejcikova stablised on her own service games, the damage was done. Sabalenka served out the match without dropping a point, capping her triumph with an ace. 

Data Slam: Sabalenka top winner on Tour

The victory was Sabalenka's 43rd match win of the year against 14 losses, breaking a tie with Krejcikova (42-11) and Ash Barty (42-8), both of whom have won grand slam titles this season, for the most WTA Tour wins in 2021. 

WINNERS/UNFORCED ERRORS

Krejcikova – 14/29
Sabalenka – 22/23

ACES/DOUBLE FAULTS

Krejcikova– 4/5
Sabalenka – 6/7

BREAK POINTS WON

Krejcikova – 1/6
Sabalenka – 4/10

Barbora Krejcikova explained she was hit by breathing difficulties and a spell of severe dizziness as she overcame Garbine Muguruza at the US Open.

French Open champion Krejcikova – who is making her main-draw debut at Flushing Meadows – had to hold off a fightback from former world number one Muguruza on Sunday to progress into her first US Open quarter-final with a 6-3 7-6 (7-4) victory.

However, Muguruza was left angry after Krejcikova started to take more time in between points.

After saving three set points at 4-5 down in the decider, Krejcikova went off court for medical treatment, before returning to see out the match on a tie-break.

Muguruza appeared to confront Krejcikova during the post-match handshake, and the Spaniard told the media: "I'll let you guys judge what you think about this.

"I think, between players, you know a little bit how to behave in certain moments and I wasn't very happy at the end of the match."

Krejcikova, however, explained how she had suffered during the match.

"I think I started the match really well and was playing good tennis," Krejcikova said, according to the WTA. 

"The key was to start the match well. There were a lot of breaks, which was difficult, but I was happy that I won the first set 6-3. Out of nowhere I got the lead 4-0 and then things started to get complicated.

"Garbine started to raise her level and I was expecting that. At the end I was really struggling and I feel really bad right now.

"I don't really know what happened, but I couldn't breathe. I started to feel dizzy and the whole world was shaking. It never happened to me before."

Krejcikova also needed medical attention after the match and did not hold a post-match news conference.

The Czech has now won 29 of her last 32 matches and will face Aryna Sabalenka, the highest seed remaining at Flushing Meadows, in the quarter-finals. 

Ash Barty reached her sixth semi-final of the year after winning the battle of grand slam champions against Barbora Krejcikova at the Western & Southern Open.

World number one and top seed Barty – the Wimbledon titleholder – dispatched French Open champion Krejcikova in straight sets in Cincinnati on Friday.

Another slam champion awaits Barty in the form of Angelique Kerber, while wildcard Jil Teichmann continued her fairytale run with victory over Olympic gold medallist Belinda Bencic.

Coffee the tonic for in-form Barty

Australian star Barty was too good for Krejcikova, winning 6-2 6-4 at the WTA 1000 tournament.

Barty had to battle from a break down in the second set against the fast-rising Krejcikova, who has shot up from 65th in the world to a career high of number 10 this year.

After extending her season record to 38-7, Barty talked about the importance of drinking coffee in the morning.

"I travel with a French press and an AeroPress, just to have two options. Usually every tournament we go to, one of us has a cafe that we have been to before, so I have got a little section of all my local cafes from the tournaments, so we try and get out to those if we can," she said.

"This year, some places we haven't been able to; some places we have. It's been nice to get some sort of a mixture, but I'm pretty simple. I'm just a black coffee cup in the morning, and then I'm set."

Three-time major champion Kerber is next up after she was 6-4 3-3 ahead before Petra Kvitova retired hurt due to a stomach problem.

Teichmann takes down another star

Unheralded Swiss and world number 76 Teichmann claimed another scalp, this time upstaging countrywoman Bencic 6-3 6-2 in the quarter-finals.

Teichmann stunned world number two Naomi Osaka en route to the quarters and maintained her giant-slaying form in Cincinnati, where 10th seed Bencic became the latest victim.

"We hugged before the match; we hugged after the match," Teichmann said of the Bencic meeting. "We know that once we step on court it's business, it's just another player I have to deal with, and she had the same mindset. At the beginning it's obviously a bit special, but once we're in it, we just look at the game, not looking at the opponent, or at least I do that way."

Teichmann will take on fifth seed Karolina Pliskova, who advanced to her second successive WTA 1000 semi-final after Paula Badosa retired down 7-5 2-0.

Ash Barty and Angelique Kerber set up a blockbuster Western and Southern Open semi-final – but Petra Kvitova suffered a fitness scare ahead of the US Open.

World number one Barty won 6-2 6-4 against French Open champion Barbora Krejcikova, who she also defeated in the fourth round during her Wimbledon title run last month.

Kerber and Kvitova then battled it out for the right to tackle Barty in the last four, but a quarter-final that was building momentum ended prematurely when two-time Wimbledon winner Kvitova found a recent stomach problem too troublesome.

Kerber was 6-4 3-3 ahead in the contest, having recovered from being an early break down in the second set, getting her game together as 31-year-old Kvitova began to suffer.

During an injury timeout, which Kvitova called after the fifth game of the second set, the Czech received a massage to her abdominal region and played on briefly, before walking up to the net to concede the match.

It remains to be seen whether the setback in Cincinnati might have consequences for her involvement at Flushing Meadows, with the US Open due to begin on August 30.

Kvitova wrote on Twitter minutes after coming off court: "I stayed out there as long as I could. I have been struggling with a stomach issue for several days and unfortunately couldn't finish the match today. Good luck Angie - sorry to end it that way - and can't wait for the next battle with you."

Kerber said in an on-court interview: "Of course, this is not the way you would want to win the match. I hope Petra will recover as fast as possible and be ready for the US Open.

"I know she's a big fighter and fights until the last points, so I hope she is not too bad and hope she is fine really, really soon."

Kerber has now won 14 of her last 15 matches, with the exception being her Wimbledon semi-final defeat to Barty.

Barty got through in a more routine manner on Friday, albeit having to battle from a break down in the second set against the fast-rising Krejcikova, who has shot up from 65th in the world to a career high of number 10 this year.

Barty said: "Barbora served exceptionally well early in that second set and was able to take advantage of a service game of mine where I just hit too many second serves.

"I wanted to try and get a little bit more positive on her service games and then try to get myself in the points a little bit more. I'm happy to run away with that one in the end."

Petra Kvitova was one of a handful of seeded players to take the court at the Western and Southern Open on Monday and came away victorious against a past champion of the event. 

The 11th-seeded Kvitova defeated 2019 Western and Southern winner Madison Keys 7-5 6-4 on a rain-plagued opening day of main-draw play at the tournament outside Cincinnati, Ohio. 

The Czech saved eight of nine break points against her serve while breaking Keys three times, and that was enough to pull out the victory. 

Kvitova's countrywoman Barbora Krejcikova, the ninth seed, made her singles debut at the WTA 1000 event with a 6-3 6-2 rout of Daria Kasatkina. 

Fifteenth seed Elise Mertens also was a straight-sets winner, taking down Nadia Podoroska 6-3 6-4, while 13th seed Jennifer Brady defeated Ekaterina Alexandrova 6-3 7-6 (7-3) in a match that finished shortly before 1 a.m. local time.

Though only Krejcikova was in action Monday, the field in Cincinnati includes nine of the top 10 players in the rankings, led by Ashleigh Barty and Naomi Osaka in their first appearances since the Tokyo Olympics. 

In other matches on the first day of play, Heather Watson defeated Aliaksandra Sasnovich 6-2 3-6 6-1, while Paula Badosa outlasted Petra Martic 4-6 6-4 7-6 (11-9) in a two-hour, 34-minute marathon. 

Yulia Putintseva breezed past Zhang Shuai 6-2 6-0, Jelena Ostapenko beat Tamara Zidansek 7-5 6-1 and Jil Teichmann downed Sorana Cirstea 6-2 6-0. 

Angelique Kerber beat Maria Sakkari 6-2 6-2, with Alison Riske matching that scoreline in a defeat of Leylah Fernandez.

Shelby Rogers won 6-4 2-1 when her countrywoman Danielle Collins retired with an injury. 

Alexander Zverev followed up his stunning win over Novak Djokovic by storming to Olympic gold in the men's singles final.

A thumping 6-3 6-1 victory against Russian Olympic Committee's Karen Khachanov was the perfect way for world number five Zverev to land the biggest title of his career.

He won 10 of the last 11 games of his semi-final against world number one Djokovic and carried that form into Sunday's title match, brushing aside the threat across the net.

It makes him Germany's first men's singles champion at the Olympics. Steffi Graf won the women's title as part of a calendar Golden Slam in 1988, and four years later Boris Becker and Michael Stich teamed up to take doubles gold.

For the man who won the ATP Finals in 2018 and reached last year's US Open title match, this marked a step forward in a career many expect will eventually feature grand slam titles.

He secured a swift break in the first set against Khachanov, who was outstanding in the semi-finals against Pablo Carreno Busta but could not impose his game in the gold-medal match.

Another break followed and the set was gone in 43 minutes.

The second set rushed by in a mere 36 minutes, with Zverev against striking early and never looking back.

He created two break points in the second game of that set, and although Khachanov saved them, a third soon followed and the Russian netted on the forehand.

The momentum was all one way and there was never a moment when Khachanov, ranked 25th by the ATP, looked as though he might pose some danger. 

Zverev gave himself a first match point when he punched away a backhand volley, and the glory belonged to the German when Khachanov slapped a forehand into the net on the next point.

BENCIC DENIED GOLDEN DOUBLE

Belinda Bencic was the surprise champion in the women's singles and the Swiss had a chance to land a second gold medal on Sunday when she and Swiss partner Viktorija Golubic lined up in the doubles final.

It was not to be for Bencic and Golubic, however, as they were soundly beaten by the prolific Czech pair of Barbora Krejcikova and Katerina Siniakova.

A 7-5 6-1 win for the reigning French Open champions meant Bencic and Golubic were left with the silver medal.

But there was little in the way of regret for the Swiss pair, with Bencic showing off both her gold and silver medals after the match, saying: "We are overjoyed. We will fly back on Monday with other medallists. It's a great feeling to know people are waiting and they acknowledge the medals we won for our country.

"The week here was incredibly beautiful. We experienced so many emotions, and it's great to go back and share all of these emotions with everyone at home.

"It's not just about the medals or the titles, it's about the memories you create that will last forever. To share this with Viki is unbelievable.

"The whole week I never felt like I was in a normal tournament or playing alone. She was alongside me the entire way. I always tell her we won this gold medal together as well. When we will be 80 years old and have a coffee, we will talk about this moment and I cannot wait for that."

Naomi Osaka was never preordained to win gold at the Tokyo Olympics but it had felt that way until she ran into Marketa Vondrousova.

The surprising 6-1 6-4 loss that a lacklustre Osaka suffered on Tuesday could be explained away by the fact the 23-year-old had not played any competitive tennis since pulling out of the French Open at the end of May.

All the same, it was a major upset as world number 42 Vondrousova took out the highest remaining seed in the draw – the Japanese star who lit the Olympic cauldron on Friday.

Osaka's exit, after previous shock defeats for top seed Ash Barty and number three Aryna Sabalenka, has raised the prospect of a shock champion, just as occurred five years ago at the Rio Games when Monica Puig of Puerto Rico caused a sensation.

Now at the quarter-final stage, there is one former grand slam champion left in the field and two finalists at that level, but it really looks like anyone's title.

VONDROUSOVA SENSES AN OPPORTUNITY

It was remarkably straightforward for Vondrousova at Ariake Tennis Park, as she cruised through the opening set and soon reeled in Osaka's early break in the second.

Osaka saved two match points when serving to stay in the contest, but not a third, planting a backhand wide.

Considering Vondrousova reached the French Open final two years ago, in front of packed grandstands rather than the empty seats in Tokyo, it was no surprise she hesitated when asked whether this win over Osaka was the biggest of her career. It probably doesn't have that cachet, good a win though it was.

"Of course it's one of the biggest," Vondrousova said.

"Naomi is a great player, she has so many grand slams, so I knew it would be a tough match. But I'm just very happy with my play. I played amazingly in the first set, and then the second set was really tough. I'm just happy to be through.

"I think she was struggling a bit with my serving. Also, I use drop-shots very well. I'm just very happy with my game today."

She faces Spain Paula Badosa next and said: "It's very open now. I think every girl is playing really well. Now it's the quarter-final, so we'll see."

HAS SVITOLINA'S TIME ARRIVED?

A fixture in the top 10 over recent seasons, Svitolina has been unable to transfer her regular tour form onto the major stage on a consistent basis.

Maybe the Olympics will be a platform towards success on that stage, with Svitolina now the highest seed remaining in the draw, at number four. The Ukrainian is also on a high on the personal front, having married French tennis star Gael Monfils shortly before heading to Tokyo.

Two semi-finals, at Wimbledon and the US Open in 2019, have been her deepest runs in the majors, and this season has been one of diminishing returns, with a fourth-round run in Australia followed by a third-round Roland Garros exit and a round-two loss at Wimbledon.

Svitolina beat Maria Sakkari of Greece 5-7 6-3 6-4 on Tuesday, setting up a quarter-final against Italian Camila Giorgi who won 6-4 6-2 against Wimbledon runner-up Karolina Pliskova.

"I don't think I'm a favourite because there are lots of good players here and everyone is quite equal," Svitolina said.

A MUG SHOT?

Should Spain's Garbine Muguruza be considered the favourite from this point? With French Open and Wimbledon titles in her trophy room, Muguruza has shown she has what it takes to triumph on a big stage, and a clinical 6-4 6-1 win over Belgian Alison Van Uytvanck on Tuesday was just the job.

She goes on to face Elena Rybakina of Kazakhstan, who edged past Croatian Donna Vekic.

Belinda Bencic of Switzerland caused a surprise by ousting the in-form reigning French Open champion Barbora Krejcikova, springing a 1-6 6-2 6-3 win that means there will be no repeat of the Roland Garros final in the quarter-finals.

That had been on the cards, but Bencic will be the player who takes on Anastasia Pavlyuchenkova for a place in the final four.

Pavlyuchenkova scored an impressive 6-1 6-3 victory over Sara Sorribes Tormo of Spain, the player who knocked out Barty in round one.

Russian Olympic Committee's Pavyluchenkova is looking to harness the form that took her to a maiden slam final, describing her Paris run as "a great experience to have".

"But every week is a new week and this is a new event," said the 30-year-old. "The Olympic Games is a very special event. It's different. It's nothing like the others."