World number 18 Reilly Opelka is through to the semi-final of the US Men's Clay Court Championships in Houston after defeating qualifier Gijs Brouwer 6-3 7-5.

The giant American, who measures in at six-foot-11, was terrific in the opening set, winning 84 per cent of his successful first serves (16-19) and allowing no break point opportunities.

The second set was much more competitive, as Brouwer broke first to go up 3-1, but Opelka answered instantly and then grabbed the match-winning break when 6-5 up to avoid a tie-breaker.

Opelka will face a fresh Nick Kyrgios in the semi-final after the Australian was gifted a walkover win against Michael Mmoh due to injury.

In a clash between two top-five seeds, world number 29 Christian Garin got the better of world number 13 Taylor Fritz 6-2 6-7 (5-7) 6-3.

What made Garin successful in the first and third sets was his return game, winning more than half of his return points in those sets combined (26-51).

Fritz had chances to get back into the game, but Garin saved 11 of 14 break point opportunities, including six of seven in the deciding third set.

Garin will play American John Isner in the semi-final after Isner triumphed in a three-set battle against Frances Tiafoe 6-4 2-6 6-3.

Isner's trademark serve was inconsistent, and abandoned him in a grim second-set performance, winning just 11 of 21 service points on his way to getting broken twice to allow Tiafoe to force the match into a third frame.

In Isner's two successful sets, he won more than 80 per cent of his first serves (35-41), and allowed no break point opportunities in the third.

David Goffin moved within a match of his first ATP Final in over a year after fighting back to beat Roberto Carballes Baena 6-7 (6-8) 6-4 6-0 at the Grand Prix Hassan II.

The former world number seven saw off the Spaniard in a three-set quarter-final to book his place in the last four, 14 months on from his last title in the Open Sud de France.

Goffin, ranked 74th in the world and unseeded for the event in Marrakech, was forced to fight across a gruelling first set, which Baena edged out in a tie-break.

But he fought back to level things in the second before sweeping through the third set unanswered.

Goffin will face Argentine Federico Coria following the latter's 6-7 (1-7) 6-1 6-4 comeback win over Richard Gasquet.

Elsewhere, Alex Molcan's run continued after the Slovakian won 4-6 6-3 6-4 against Botic van de Zandschulp following his last-16 victory over top seed Felix Auger-Aliassime.

He will now face Laslo Djere in the last four after the Serbian overcame Italy's Lorenzo Musetti in straight sets.

Novak Djokovic could face Carlos Alcaraz for the first time after the Monte Carlo Masters draw put the world number one and the teenage revelation on course to clash in the quarter-finals.

The draw for the tournament that begins on Sunday served up the appetising prospect of a tussle between the reigning French Open champion and a player many expect to enjoy huge Roland Garros success.

Alcaraz, 18, last week became the youngest men's champion at the Miami Open, and he has soared to number 11 in the ATP rankings after sitting outside the top 100 at this time 12 months ago.

He won an ATP 250 tournament on clay last year in Umag, and an ATP 500 on the surface in Rio de Janeiro in February, but earning a Masters 1000 hard court title in Miami highlighted the scale of Alcaraz's rapid improvement.

Both he and Djokovic will receive a first-round bye in Monte Carlo, and they must then win twice to set up a meeting at the last-eight stage.

Alcaraz may have to beat the in-form Indian Wells champion Taylor Fritz in the third round, with Marin Cilic and Sebastian Korda also potential early opponents for the young Spaniard.

Djokovic will not be taking a quarter-final place for granted, either. If he navigates his opening match, the Serbian could face a dicey third-round clash with Spain's Roberto Bautista Agut or the player to whom he lost at the last-16 stage last year, Britain's Dan Evans.

Rafael Nadal is absent after suffering a stress fracture of a rib during his Indian Wells final defeat to Fritz.

Taylor Fritz saw his way past Alejandro Tabilo to advance to the quarter-finals at the US Men's Clay Court Championships, winning 6-1 6-4 on Thursday.

Fresh off his maiden ATP 1000 title at Indian Wells and fourth-round run in Miami, the American world number 13 needed just 62 minutes to win in straight sets, in his first clay court match for the season.

Fritz's serve was not particularly secure, though, with the unseeded Tabilo converting on only one of six break point attempts. Fritz was more efficient and assertive when opportunities presented on the other hand, taking two of three break point chances on Tabilo's serve while winning 12 out of 19 points returning on his second serve.

Despite the Chilean world number 100 fighting back to 4-4 from 3-0 down in the second set, Fritz steadied to close out the match.

"I felt like tonight was going to be a really tough match, given he's done really well on clay," Fritz said post-match. "It was my first match [on clay]. I'm pretty happy with how I played. I can't complain, I got out of that pretty solid."

Fritz will now face another Chilean, fifth seed and defending champion Cristian Garin, who came back from a set down to defeat Jordan Thompson 3-6 6-3 6-3.

Entering the Houston event on a five-match losing streak, Garin has come from behind in back-to-back matches to win.

Sixth seed Frances Tiafoe also went the distance on Thursday, earning a 5-7 7-5 7-6 (7-4) win over Uruguayan Pablo Cuevas.

With neither garnering break point chances in the third set, Tiafoe finally created breathing room by winning four straight points at 2-2 in the deciding tie-break, before closing out the match.

It sets up an all-American quarter-final with John Isner, who defeated Steve Johnson 6-7 (1-7) 7-6 (7-4) 6-3 in Thursday's final game.

Top seed Felix Auger-Aliassime crashed out of the Grand Prix Hassan II after he was beaten 6-4 2-6 7-6 (9-7) by world number 65 Alex Molcan.

Making his debut in Marrakech, Auger-Aliassime arrived off the back of an impressive start to 2022.

Indeed, the world number nine had already triumphed in Rotterdam and been runner-up to Andrey Rublev in Marseille.

But he came unstuck at the hands of the player ranked 56 places lower, with Molcan securing his first career win over a top-10 player.

The Slovakian crucially broke in game nine on the way to taking the opening set. Auger-Aliassime, who hit 10 double faults during the contest, responded by dominating the second, while the players exchanged breaks in a decider that went to a tie-break.

The top seed forced match point at 7-6 up, but Molcan held on by reeling off the next three to secure a dramatic victory.

David Goffin, meanwhile, claimed his 300th tour-level win as he came from behind to defeat three-time champion Pablo Andujar.

Andujar had seen off second seed Dan Evans in the first round but, despite making a fast start against Goffin, it was the Belgian who triumphed 5-7 7-6 (7-4) 6-3.

Federico Coria overcame Mirza Basic in straight sets, while Roberto Carballes Baena defeated Portugal's Joao Sousa 6-2 7-6 (7-4) and Richard Gasquet saw off Pavel Kotov.

Dominic Thiem is ready to "get back on track" after testing negative for coronavirus.

The luckless Austrian revealed he had contracted COVID-19 after making a long-awaited return in the Andalucia Open Challenger Tour event last week.

Thiem has not played on the ATP Tour since last June, missing Wimbledon and the US Open in 2021 after undergoing wrist surgery.

The 2020 US Open champion, who was beaten by Pedro Cachin on his comeback in Marbella, on Thursday stated that he is now COVID-free.

"A short update: I am finally negative and I feel much better! Thank you for all your messages! I really appreciate it!" he tweeted.

"I'm going to have a medical check-up, so I can get back on track!"

Thiem has reportedly pulled out of the Monte Carlo Masters this week, but his return to the ATP Tour should be imminent with the French Open on the horizon next month.

Matteo Berrettini could miss the French Open after the world number six was forced to withdraw from three tournaments as he continues to recover from minor hand surgery.

The Italian progressed to the Wimbledon final in 2021 and started the new season in encouraging fashion as he reached the Australian Open semi-finals, where he was well-beaten by eventual winner Rafael Nadal.

However, the 25-year-old has seemingly struggled from then on, with his next best performance coming in Rio – where he made the last eight – as he limped to a 9-6 record so far in 2022.

Further difficulties followed for Berrettini after he sustained an injury to his right hand late in March, forcing him to withdraw from the Miami Open before undergoing a "minor operation".

Berrettini provided another update on Instagram on Thursday, revealing he would not feature at the Monte-Carlo Masters, scheduled to start later this week, or the Madrid Open and Italian Open at the start of May.

The latter tournament in Rome begins just two weeks before the second grand slam of the year, leading to concerns that Berrettini may not feature at Roland Garros.

"UPDATE – following advice from the medical experts, my team and I have decided that it is crucial I do not put time pressure on my recovery process," he posted.

"We have therefore decided I should withdraw from the Monte-Carlo, Madrid and Rome tournaments to ensure I give myself the proper amount of time to return at my highest level.

"Withdrawing from these events, particularly Rome, was an extremely tough decision, however it is the right one to ensure many more years of competing at the highest level for the biggest trophies.

"Thanks very much for all the support. My recovery process is on track and I look forward to seeing you on-court soon."

The 2022 French Open will provide Jo-Wilfried Tsonga with a final opportunity to shine in front of a home crowd after the 36-year-old confirmed his impending retirement.

Tsonga has suffered with injuries over recent seasons and has managed just two ATP Tour match wins so far in 2022.

The Frenchman reached a high ranking of world number five and finished as runner-up at the 2008 Australian Open.

He never won a grand slam but did reach five more major semi-finals. Tsonga has collected 18 singles titles on the ATP Tour, including two Masters 1000 crowns in Paris (2008) and Toronto (2014). His last triumph came in 2019 in Metz.

"It is with great emotion that I announce today my decision to stop my professional career at the next French Open," Tsonga wrote on social media.

"So many incredible moments, so much joy shared with a public that gave me a lot. Hoping for one last thrill with you!"

In a video accompanying his announcement, Tsonga said: "The goal is to be myself, to be Jo-Wilfried Tsonga the tennis player.

"I hope that I will stay in shape before and be able to be who I have always been at this tournament.

"I have always set myself high goals to try to get what I can. For me, this will be the opportunity to do it one last time."

Yannick Noah (69.6 per cent) is the only Frenchman to have a higher winning percentage in tour-level matches than Tsonga (66.5).

Nick Kyrgios continued his strong return to clay courts on Wednesday, defeating Tommy Paul 6-4 6-2 to progress to the quarter-finals of the US Men's Clay Court Championships in Houston.

Before Tuesday's victory over Mackenzie McDonald, Kyrgios had not played on clay since his infamous meltdown against Casper Ruud at the Rome Masters in 2019, where he threw a chair across the court and walked off during a change of ends.

The 26-year-old Australian wild card's serve kept him in relative control, saving all six break points he faced in the 70-minute match, as well as serving 10 aces and winning 88 per cent of points on his first serve.

"I had to be locked in today and I knew that I had to serve well," Kyrgios said post-match. "It's probably one of the better matches I've played on clay in my career, so I'm pretty happy with the way I came out here today, just put my head down and went to work.

"I've been serving really well, so I just wanted to keep to good habits."

The world number 94 will now face Michael Mmoh, who defeated Sam Querrey 6-2 6-4.

Meanwhile, third seed Reilly Opelka did it relatively tougher in the other all-American clash on Wednesday, coming back from a set down to defeat Mitchell Kreuger 3-6 6-2 6-4.

Opelka came into the match having lost just 13 service games in 19 matches this season, but was broken twice in the opening set against Krueger. The world number 18 has been dealing with a right shoulder injury that forced him to retire at the Miami Open against Francisco Cerundolo.

The 24-year-old still managed 15 aces for the match, including a big serve out wide in the Ad court on match point.

"He played well, I think he came out swinging," Opelka said afterwards. "I think he was free, I wasn't. It's a different situation.

"It was a good opportunity for him to play free and get a win and I'm a guy who hasn't always been the most consistent, especially changing surfaces, so I think it was a good win."

He will face Gijs Brouwer, who progressed past J.J. Wolf with a 6-1 6-1 win.

David Goffin will go up against three-time Grand Prix Hassan II champion Pablo Andujar for a place in the quarter-finals in Marrakech.

The former world number seven is in the hunt for a first title of the season, and defeated Damir Dzumhur 6-2 7-6 (7-3) in his first match on Wednesday.

That victory teed up a last-16 tie with Andujar, who defeated second seed Dan Evans in his first-round match.

The 36-year-old Spaniard is something of a specialist in Marrakech, having won this tournament three times, in 2011, 2012 and 2018.

Young Italian prospect Lorenzo Musetti overcame Andujar's compatriot Carlos Taberner 6-1 6-7 (3-7) 6-3 to become the first player to reach the quarter-finals.

Musetti, who reached the last 16 at last year's French Open and featured at the ATP Next Gen Finals, has had a tough start to 2022, only reaching one other quarter-final so far.

Serbian eighth seed Laslo Djere followed Musetti into the last eight by beating Malek Jaziri 6-4 6-2.

Qualifier Mirza Basic sprung a surprise to overcome Kamil Majchrzak 4-6 6-4 6-1, while Vit Kopriva defeated Bernabe Zapata Miralles in straight sets.

World number 172 Pavel Kotov claimed the scalp of a top-100 player, bouncing back from a first-set bagel to beat Tallon Griekspoor 0-6 6-2 6-2.

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.