Nick Kyrgios made his return to clay with a win on Tuesday, defeating Mackenzie McDonald 4-6 6-3 6-4 at the US Men's Clay Court Championships in Houston.

It was the first time Kyrgios had played on clay since his infamous meltdown at the Rome Masters in 2019, where he threw a chair across the court and walked off, handing Casper Ruud a win by default.

After a meandering first set, the Australian world number 94 sparked into life when he saved the first of two break points with a second serve ace in the third game of the second. From there, Kyrgios opened up his shoulders and became more assertive from the baseline, as well as serving 18 aces in the closing two sets.

While again admitting clay is not his favourite surface, the 26-year-old was nevertheless pleased by the manner of the win against McDonald.

"He [McDonald] beat me in Washington where I used to play pretty well, and he's a tricky one because he doesn't make too many errors, and clay's obviously not my preferred surface," he said post-match.

"I just served really well, and just started playing more aggressive and found another gear. I would slip and slide a little bit, but my game actually suits the clay quite well."

While US seventh seed Tommy Paul secured a walkover 6-7 (4-6) 7-6 (7-5) 3-2 win against Peter Gojowczyk, Chilean fifth seed and defending champion Cristian Garin also came from a set down to beat Jack Sock 4-6 6-3 7-5.

American sixth seed Frances Tiafoe faced relatively simpler work, defeating unseeded countryman Marcos Giron in straight sets 6-4 6-4.

Two all-American matches also opened play in Houston on Tuesday, with JJ Wolf securing a 6-4 6-4 win over eighth seed Jenson Brooksby in the first, and Steve Johnson defeating Denis Kudla 6-3 4-6 6-4.

In light of recent high-profile misconduct, the ATP has warned players of harsher punishments for on-court behaviour in an internal note, as it also reviews its framework for stopping repeat offenders.

Nick Kyrgios was fined for audible obscenities and hurling his racquet onto the ground after his defeat to Rafael Nadal in Indian Wells – almost hitting a ballkid - while Alexander Zverev was thrown out of the Mexican Open in February after smashing his racquet repeatedly against the umpire's chair.

Jenson Brooksby also came under fire at the Miami Masters, throwing his racquet and hitting a ballkid in his win over Federico Coria, with Coria also motioning during the match that the consequent point penalty was not sufficient.

The recent spate of on-court outbursts has prompted the ATP to act.

"Effective immediately and as we head into the clay court swing, the ATP officiating team has been directed to take a stricter stance in judging violations of the Code of Conduct," ATP Tour chief Andrea Gaudenzi wrote in a circular to the players.

"Additionally, we are also undertaking a review of the Code, as well as the disciplinary processes, to ensure that it provides appropriate and up-to-date penalties for serious violations and repeat offenders."

Kyrgios was also fined after his loss to Jannik Sinner in Miami for criticising the umpire and smashing his racquet, and although Zverev was handed an eight-week suspension for his outburst in Acapulco, the ATP appears determined to nullify future misconduct.

While Gaudenzi, the Italian former top 20 player, understood the human elements to players competing under extreme pressure, he asserted the game itself should be taken into consideration.

"The first three months of the season have seen an unusual frequency of high-profile incidents involving unsportsmanlike conduct," Gaudenzi wrote.

"These incidents shine a bad light on our sport. This conduct affects everyone, and sends the wrong message to our fans, especially young fans."

Top seed Felix Auger-Aliassime cruised through his debut match at the Grand Prix Hassan II as Dan Evans crashed out in the first round.

World number nine Auger-Aliassime needed just an hour and 24 minutes to see off home hope Elliot Benchetrit 6-3 6-3.

He saved all six break points he faced to set up a second-round meeting with Slovak lefty Alex Molcan in Morocco.

But Evans' stay in Marrakech is over after he succumbed to a surprise 6-4 6-2 loss to Pablo Andujar. The Briton has now won just one of his last five matches on tour.

Lorenzo Musetti has endured a tough start to 2022 and headed into this tournament 5-7 on the year.

However, the 20-year-old delivered a reminder of his potential with a straight-sets win over fourth seed Albert Ramos-Vinolas.

Joao Sousa knocked out fifth seed Federico Delbonis but sixth seed Botic van de Zandschulp and eighth seed Laslo Djere did prevail, as did veteran Richard Gasquet.

Carlos Alcaraz said he never expected to have such a meteoric rise so early in his career after winning his first ATP Masters 1000 title at the Miami Open.

Alcaraz defeated Casper Ruud 7-5 6-4 in the final, making the 18-year-old the youngest ever winner in Miami, beating Novak Djokovic's previous record when he won it aged 19.

With the win, Alcaraz jumped all the way up number 11 in the world.

Speaking to Tennis Channel after his triumph, Alcaraz said he has already exceeded his goals for this season.

"Of course, I did not expect this," he said.

"My goal was to end this year in the top-15, and now I'm at 11, close to the top-10. I'm going up so fast, and I think it's [because of] all the hard work I'm putting in every day.

"Of course my experience from last year has helped me a lot – playing Rafa (Nadal) in Madrid, against (Alexander) Zverev in Acapulco – you have to live that experience to learn.

"When I started playing tennis when I was five or six, I wanted to be number one in the world, and this year I've realised I can beat the top players in the world."

Alcaraz was buoyed by the presence of his coach, former world number one Juan Carlos Ferrero, who surprised him the day before the final after being absent throughout the tournament, mourning the death of his father back in Spain.

"Juan Carlos [Ferrero] played everything that I'm playing, he has experienced all that I am experiencing right now, so he has helped me a lot," he said.

"It's amazing to have Juan Carlos here with me – I talk with him every day, but it was a surprise when he arrived, I didn't know anything.

"It was a big surprise and I was really happy [to see him] – I'm really happy to win my first Masters 1000 title with him here."

With the young Spaniard now drawing comparisons to Spanish superstar Rafael Nadal, Alcaraz said it can only be a good thing.

"If people are comparing you with Rafa, that means you are doing great things, and you are doing it the right way," he said.

"I'm trying to not think about that – Rafa is Rafa, and I am Carlos Alcaraz – Rafa is one of the best players in the history of tennis, and I am a young man living his dream.

"I looked up to Rafa when I was young, he inspired me a lot, watching his big matches, so to be around him in the tour, and to be able to play against him, is pretty special."

Carlos Alcaraz became the youngest Miami Open men's champion as the teenage Spaniard continued his rapid rise by fending off world number eight Casper Ruud.

A 7-5 6-4 victory in Sunday's final gave 18-year-old Alcaraz the third ATP singles title of his career, after winning the 2021 Croatia Open and the Rio Open in February this year.

Alcaraz's maiden Masters 1000 title saw him secure Miami glory even earlier than Novak Djokovic, who was 19 at the time of his 2007 triumph.

"I have no words to describe how I feel – it feels so special to win my first Masters 1000 here in Miami," Alcaraz said.

While he got the job done in the end, there was far from a smooth start for Alcaraz, who lost the first three games of the opening set as Ruud grabbed the early break.

Down 4-1 in that first set, Alcaraz then rattled off three consecutive games to tie it back up, and after breaking again to go up 6-5, he held his nerve to save a break point and move ahead in the contest.

Ruud had issues dealing with Alcaraz's first serve all match long, but it was most dominant in the first set, the Spanish player winning 76 per cent when landing his first serves, while Ruud was down at 54 per cent.

Alcaraz flipped the script in the second set and jumped out to a 3-0 lead with a double break. Ruud was able to get one break back, but he never threatened the rest of the way as Alcaraz closed it out in style, conceding only two points from his last three service games.

Speaking on the court after his win, Alcaraz was overjoyed as he acknowledged a large contingent of support in the crowd, including coach Juan Carlos Ferrero.

"I have my whole team with me, and my family… this is the second tournament that they've all been here with me," he said.

"Thank you to my team, I'm glad to have my father here with me and to be able to share this moment with my family."

Touching on some of his strategy, Alcaraz said the plan was to try and avoid Ruud's dominant forehand as much as possible.

"I knew Casper is playing unbelievable, and has a big forehand, so I tried to play to his backhand first, and attack all the time," he said.

"I'm always trying to attack, and not let him dominate the match with his forehands down the line – that was a pretty big key for me."

With the win, Alcaraz becomes the world number 11, and does not turn 19 until next month.

Daniil Medvedev has confirmed he will undergo a procedure to fix a troubling hernia issue, which may keep him out of the French Open.

Medvedev, who enjoyed a short-lived stint as world number one at the start of March before relinquishing the crown back to Novak Djokovic, reached the quarter-finals at Roland Garros last year.

However, the chances of the Russian appearing in Paris now seem slim, given he faces up to two months out of action following the impending operation.

This year's French Open runs from May 22 until June 5.

"Hi everyone," the world number two tweeted on Saturday. "The last months I have been playing with a small hernia.

"Together with my team I have decided to have a small procedure done to fix the problem. I will likely be out for the next 1-2 months and will work hard to be back on court soon. Thanks for all the support."

Medvedev had been hoping to use the clay court swing to reclaim top spot in the ATP rankings.

He could have done so had he reached the semi-finals of the Miami Open last week, yet the 26-year-old lost 7-6 (9-7) 6-3 in the quarters to Hubert Hurkacz.

Medvedev appeared to be struggling in that tie and after the defeat he told reporters: "All the match I was not feeling my best. But, you know, sometimes it happens.

"I don't know the actual reason. Maybe the heat. But I was feeling super, like, dizzy, tired, and there was this long game where I couldn't serve anymore.

"Then in the locker room I was cramping quite much, so physically was not easy. But at the same time, that's part of the game."

Should Medvedev fail to return in time to make the season's second grand slam, the reigning US Open champion will hope to be fully firing by the time Wimbledon comes around in late June.

Daniil Medvedev missed the chance to return to the top of the rankings as he was beaten by Hubert Hurkacz in the quarter-finals of the Miami Open on Thursday.

Medvedev would have become world number one once again if he had defeated Hurkacz, but the defending champion won 7-6 (9-7) 6-3 on Hard Rock Stadium.

Novak Djokovic will remain the top-ranked male player on the planet thanks to Pole Hurkacz, who levelled his head-to-head record with the Russian at 2-2.

Carlos Alcaraz or Miomir Kecmanovic will do battle with eighth seed Hurkacz, who won 74 per cent of points on his first serve and broke Medvedev's serve three times, for a place in the final.

Hurkacz's win over the top seed was his second against a top-two player, with the first also coming against Medvedev at Wimbledon last year.

"I think the return was crucial. I was able to make a lot of returns and get some free points on my serve, because having rallies with Daniil is fun, but they get long,” Hurkacz said on his on-court interview.

"It is good I was able to get some free points. I have spent a lot of time in Florida, so I am used to the humidity. I think the conditions were in my favour today, so I tried to use them."

Casper Ruud set up a semi-final with Francisco Cerundolo at the Miami Masters after he defeated Alexander Zverev 6-3 1-6 6-3 on Wednesday.

Ruud's heavy topspin game gave Zverev problems initially, contributing to a 94 per cent success rate from points on his first serve, while Zverev struggled to find rhythm on serve at 58 per cent.

Saving two break points in the opening game of the second seemed to spark Zverev into life, but Ruud was able to regroup and continue dominating from the baseline in the third to comfortably see his way through.

"It was great to get that break early on [in the third set] and I was able to keep it all the way out," Ruud said post-match. "I was serving well. I can thank my serving for the win today."

The Norweigian world number eight lost his first three ATP 1000 quarter-finals on hard court, but played with confidence on the back of a 75 per cent first-serve rate.

He will face Cerundolo, who also advanced into the semi-finals on Wednesday, after Jannik Sinner was forced to retire due to foot blisters. The Argentine was leading 4-1 in the first set after 23 minutes when Sinner called the match.

The world number 103 held a 0-2 record on hard courts prior to this week, but has now made his first ATP 1000 semi-final in as many attempts after progressing past Tallon Griekspoor, Reilly Opelka, Gael Monfils and Frances Tiafoe.

Cerundolo has enjoyed a strong start to 2022, with respective quarter-final and semi-final appearances on clay in Buenos Aires and Rio de Janeiro.

The winner of the upcoming semi-final will make their first ATP 1000 final appearance, while Ruud was able to beat Zverev at third time of asking, losing the opening two games head-to-head.

Dominic Thiem's bad luck continued as the former world number three confirmed he has tested positive for COVID-19.

Thiem only made his return to action on Tuesday, having not featured on the ATP Tour since June last year.

The Austrian underwent surgery on a wrist injury that kept him out of Wimbledon and also prevented him from defending his US Open title, while he also missed this year's Australian Open.

Having opted to push back his comeback further by skipping Indian Wells and the Miami Open, Thiem instead decided to play at the Challenger Tour's Andalucia Open.

His return was short-lived, as Thiem went down 6-3 6-4 to Pedro Cachin.

And Thiem will now face another spell out, after revealing he has contracted coronavirus.

"Looks like lately the good news don't last long... last night after dinner, I started feeling unwell and didn't have a good night," Thiem wrote on his official Instagram account.

"After developing mild symptoms I decided to take a test this morning, which came back positive for COVID-19.

"Now I have to wait and see how it develops. I'll keep you posted. Thank you all in advance for your support!"

Former US Open champion Dominic Thiem made his long-awaited return from a wrist injury on Tuesday, but lost 3-6 4-6 to Pedro Cachin at an ATP Challenger event in Marbella.

Thiem, the former world number three who hasn't played since 2021, started slowly and fell 5-0 behind in the first set against the world number 228.

He improved in the second set but was not able to recover from dropping serve in the first game.

"Obviously, the result today is the bitter part," Thiem posted on his Instagram. "I would have wanted to win, and I have to accept the defeat in a humble manner.

"This is only the beginning of a long way to the top of my game."

Emerging Spanish star Carlos Alcaraz continued his rise with a 7-5 6-3 upset of third seed Stefanos Tsitsipas to reach the Miami Masters quarter-finals on Tuesday.

The 18-year-old, who reached last year's US Open final eight after beating Tsitsipas in the third round, proved too good again for the Greek in one hour and 50 minutes.

Alcaraz reached last week's Indian Wells semi-finals and is now 15-2 on the season, with the win setting up a clash with Serbian Miomir Kecmanovic who upset last week's Indian Wells champion Taylor Fritz 3-6 6-1 6-4.

Tsitsipas broke the Spaniard in the sixth game and led 5-2 before Alcaraz reeled off seven straight games to sensationally take the first set.

Alcaraz surged ahead in the second set, with his defence and speed leaving Tsitsipas short on answers.

The Spaniard, who saved seven of eight break points throughout the match, converted his fourth match point for victory.

"It was really, really tough. He was playing unbelievable," Alcaraz said after the match. "All I can say is I fought until the last ball in the first set [to] come back."

Ninth seed Jannik Sinner won 7-6 (7-3) 6-3 over enigmatic Australian Nick Kyrgios, who had a furious outburst directed at umpire Carlos Bernardes.

The Australian was heard to label Bernardes "an absolute clown" and continued to berate the umpire late in the first set, leading to a code violation and two penalties.

Kyrgios completely lost his cool, demanding to speak to a tournament official before smashing his racquet early in the second set, leading to a game penalty as well.

Sinner will next take on Argentine Francisco Cerundolo after he defeated 28th seed Francis Tiafoe lost 6-7 (2-7) 7-6 (7-3) 6-2.

Top seed Daniil Medvedev made light work of Jenson Brooksby 7-5 6-1 to set up a quarter-final showdown with reigning champion Hubert Hurkacz who won 7-6 (7-3) 6-2 over Lloyd Harris. Medvedev will return to the top of the ATP rankings if he wins their quarter-final.

Second seed Alexander Zverev got past Thanasi Kokkinakis 6-4 6-4 and will meet sixth seed Casper Ruud in the last eight, after the Norwegian won 6-3 6-4 over Briton Cameron Norrie.

Nick Kyrgios called on the ATP Tour to "get new people" after a furious outburst at the umpire in his defeat to Jannik Sinner at the Miami Open.

Kyrgios berated umpire Carlos Bernardes after his walkie-talkie went off mid-point during the first set.

The Australian was heard to label Bernardes "an absolute clown".

He subsequently added: "This is one of the biggest tournaments and you guys can't do your job. It's embarrassing.”

"You wonder why no one watches this sport. It's a laughing stock."

After receiving a code violation for an audible obscenity, Kyrgios was then handed a point penalty for unsportsmanlike conduct in the first set tie-break.

Kyrgios had been appearing to talk with a friend in attendance courtside, with that penalty further infuriating him.

"What's unsportsmanlike? What is unsportsmanlike?" Kyrgios asked of Bernardes.

He then demanded to see a tournament official before smashing his racquet during the opening game of the second set, an action that saw him cop a game penalty and drop his serve.

Sinner maintained the initiative from there, easing to a 7-6 (7-3) 6-3 win, with Kyrgios' mind clearly still focused on the performance of the official even after the dust had settled.

He posted on Twitter: "'You could do the job of the umpire' - what was said to my best friend that got me 'unsportsmanlike code violation' at 5-3 in the first set tie break.

"With 100 of thousands of dollars on the line that was the decision he made because the umpire's feelings got hurt. GET NEW PEOPLE"

The Miami Masters' top seed, Daniil Medvedev, had no problems making his way past Spain's Pedro Martinez 6-3 6-4 to earn his spot in the fourth round.

Serving was the story of the match as the world number two tallied up 14 aces to his unseeded opponent's zero, and only allowed Martinez to see five second serves in the opening set, with Zverev winning all five. Overall, Zverev won 20 of 24 points on serve in the first set.

The second set was more competitive, with Martinez even breaking back after Zverev jumped ahead and looked to coast to victory, but he could not hold off the Russian down the stretch.

Medvedev will play American Jenson Brooksby in his fourth-round matchup after he won a hard-fought 6-3 5-7 6-4 struggle against 15 seed Roberto Bautista Agut.

In a razor-close contest, Brooksby was just slightly better throughout, winning 60 per cent of his service points compared to the Spaniard's 59 per cent, as well as winning 41 per cent of return points compared to Bautista Agut's 40 per cent.

Fresh off his Indian Wells Masters triumph over Rafael Nadal, Taylor Fritz kept his good form going with a 7-6 (7-2) 6-4 win against American compatriot Tommy Paul.

Fritz, who is now up to world number 13, did not have his serve broken all day, winning 81 per cent of his successful first serves (30-37), while also capitalising on the only two break points he saw.

14 seed Carlos Alcaraz only needed two sets to get past 21 seed Marin Cilic 6-4 6-4, creating nine break point opportunities to Cilic's one, which was saved.

In the late session, and in a meeting of rapidly rising prospects, 22-year-old Serbian Miomir Kecmanovic pulled off an upset 7-6 (7-4) 6-3 win over 21-year-old American Sebastian Korda.

Meanwhile, three seed Stefano Tsitsipas was too much for Australian Alex de Minaur, winning 6-4 6-3 after allowing no break point opportunities in the opening set, and saving all three in the second.

Ivan Lendl insists Andy Murray can still compete for grand slam titles after re-joining the Scot's coaching team for a third time.

Lendl has teamed up with Murray in order to prepare the two-time Wimbledon champion for his home grand slam this summer, with the 34-year-old skipping the clay-court season to enhance his chances of being at his best on the grass.

Murray won all three of his grand slam titles, Wimbledon in 2013 and 2016, and the US Open in 2012, under Lendl's guidance, but has not reached a grand slam quarter-final since 2017, undergoing two hip surgeries during that time.

Lendl, who himself won eight grand slams during a glittering playing career, cited Rafael Nadal's victory in January's Australian Open as evidence that class remains permanent, and expressed confidence in Murray's ability to follow his lead.

"You are asking this [whether Murray can compete] with a straight face after what Rafa [Nadal] has done in Australia," Lendl said after watching Murray's second-round defeat to Daniil Medvedev in Miami.

"They are just like bulldogs, and they want to do things because they haven't been done before.

"If they set their mind to it then they can achieve amazing things.

"Rafa said he wasn't even sure he's going to be able to play again [after his own injury problems], then he goes and wins the Australian Open. So yes, these guys can do it.

"I would say grass is probably Andy's best surface. 

"[For] a lot of the players, it's their worst surface. That would obviously increase his chances." 

Murray made his first ATP final since 2019 earlier this year, losing in straight sets to Aslan Karatsev in the final of the Sydney International in January, and is 85th in the ATP world rankings.