Alexander Zverev has apologised for his outburst at the Mexico Open that saw him "withdrawn" from the singles competition for attacking an umpire's chair. 

Zverev and Brazil's Marcelo Melo were in a super tie-break against Lloyd Glasspool and Harri Heliovaara when they were angered by a call made by the umpire, who overruled a decision from the line judge.

Glasspool and Heliovaara subsequently profited by delivering an ace on match point, which was followed by Zverev quickly walking off and smashing his racquet against the umpire's chair three times.

The world number three then shouted at the umpire that he had "destroyed the whole f****** match" before striking the chair again.

Zverev was due to be in second-round singles action against Peter Gojowczyk, but the ATP Tour confirmed the Olympic champion had been removed from the draw due to "unsportsmanlike conduct".

Former world number one Andy Murray condemned the 24-year-old's "reckless" outburst after his loss to Jannik Sinner, and Zverev has now apologised unreservedly for his raging response.

"It is difficult to put into words how much I regret my behaviour during and after the doubles match yesterday," Zverev wrote on Instagram on Wednesday. 

"I have privately apologised to the chair umpire because my outburst towards him was wrong and unacceptable, and I am only disappointed in myself. 

"It just should not have happened and there is no excuse. I would also like to apologise to my fans, the tournament, and the sport that I love.

"As you know, I leave everything on the court. Yesterday, I left too much. I am going to take the coming days to reflect – on my actions and how I can ensure that it will not happen again. I am sorry for letting you down."

Lewis Hamilton insisted Formula One must ensure that there is no bias from stewards heading into the 2022 season.

Hamilton was beaten by Red Bull's Max Verstappen in a contentious conclusion to the Abu Dhabi Grand Prix, after race director Michael Masi elected to allow a series of cars to pass a late safety car, permitting one lap of racing with the Dutchman on new tyres.

Masi has since been removed from his role, while rumours abounded that Hamilton could leave the sport, though the seven-time world champion last week confirmed he would be racing once again for Mercedes this season.

Two new race directors will share the role Masi has vacated.

At the first testing session in Barcelona ahead of the new campaign, which starts on March 20 in Bahrain, Hamilton was asked if the changes would result in more consistent decision-making.

"We need to make sure we have non-biased stewards, too," the 37-year-old said.

"Racing drivers, some are very good friends with certain individuals, some travel with certain individuals and tend to take more of a keen liking to some of them.

"I think [we need] people who have no bias, are super central when it comes to making decisions."

Hamilton's belief is not shared by his team's boss, Toto Wolff, however.

"I think we need professionalism in the stewards' room," said Wolff in a news conference.

"I don't think there is a conscious bias to be honest. It's intelligent people."

Red Bull's Christian Horner, who has a not-so-secret rivalry with his Mercedes counterpart, agreed.

"I would agree with Toto that I don't think there's an intended bias. I'm not aware of any stewards travelling with drivers to races," he added.

"In [FIA president] Mohammed [ben Sulayem] we have a new president that is looking to bolster the structure and bring in an equivalent of a VAR [video assistant referee, used in football], and I think giving a better infrastructure for clearer decisions with clearer regulations is something that should be strived for.

"But I certainly don't think there was any bias from any stewards during the last seasons."

Ireland will be without Iain Henderson for their home clash with Italy in the Six Nations after he tested positive for COVID-19.

Andy Farrell's side sit third in the table after a 29-7 triumph over Wales preceded a 30-24 loss to leaders France in the second round.

Ireland host winless Italy at the Aviva Stadium in Dublin on Sunday, but they will not have second rower Henderson to call upon after confirming the 30-year-old has contracted the virus.

Another spell on the sidelines will frustrate the Ulster captain, given he only returned from injury off the bench in the loss against France.

Henderson, who captained his country for the first time in February 2021, will now serve a period of self-isolation at home and will likely return for meetings with England and Scotland in March.

Ireland confirmed there were no other positive results within the squad and the group will continue to complete routine tests across the week.

Farrell will still have Tadhg Beirne, James Ryan, Kieran Treadwell and Ryan Baird as second-row options and has not yet called up a replacement for Henderson.

With another NBA All-Star weekend in the books, Thursday sees the league back in regular season action, with one of the more intriguing games taking place at Barclays Center when the Brooklyn Nets entertain the Boston Celtics.

They played in the same venue earlier this month, with Boston easing to a 126-91 victory, which the Nets will be eager to avenge this time.

Somewhat surprisingly given the strength of their respective rosters, Celtics star Jayson Tatum was the only player representing either team to play in the All-Star game, scoring eight points during his 20 minutes on court for Team Durant.

Kevin Durant missed the game in Cleveland with a knee injury and is likely to be out of this clash as well. 

Nets general manager Sean Marks recently said Durant and new arrival Ben Simmons could be ready to play in the coming weeks, but the visit of the Celtics is likely to come too soon for both.

Steve Nash's team currently sit eighth in the Eastern Conference on 31-28, having fallen away dramatically in the last month, losing 11 games in a row until beating the Sacramento Kings on Valentine's Day.

Injuries have played a big part in the dip in form, but back-to-back wins against the Kings and the New York Knicks suggested they could be about to turn things around, even with a defeat to the Washington Wizards in their last game before the All-Star break.

The Celtics, meanwhile, have been going in the other direction, winning nine games in a row before a loss to the Detroit Pistons ahead of the break, and they find themselves sixth in the East on 34-26.

Coach Ime Udoka has led his team to a five-game winning streak on the road and will be looking to make it six in Brooklyn.

He will be reliant on Tatum and Jaylen Brown to pick up where they left off. The Celtics' star duo combined for 57 points and 20 rebounds in the recent 135-87 thrashing of the Philadelphia 76ers.

The impact of guard Derrick White could also be crucial after his recent arrival from the San Antonio Spurs. He has made a respectable start to life with Boston, averaging 12.3 points per game in his four outings.

The restart of the league signals the beginning of what will no doubt be a tense run in a tightly contested Eastern Conference, and both these teams will be looking to get off to a perfect start on Thursday.

PIVOTAL PERFORMERS

Brooklyn Nets – Patty Mills

It's a home game, so Kyrie Irving (vaccination status) cannot play, and with James Harden gone and no Durant or Simmons yet, the pressure will once again fall on Mills to be his team's main man.

The Australian narrowly missed out on the three-point finals at All-Star weekend but is enjoying a career-best season for points (13.4 average per game) in Brooklyn after moving from San Antonio last year.

His three-point shooting is what has been letting him down in recent times, going five games in a row scoring single figures for points, before hitting 22 in the loss to Washington before the All-Star break, including five of seven from beyond the arc.

Boston Celtics – Jayson Tatum

Tatum has been his team's standout player this season, and the momentum from featuring in the All-Star game could see him raise that level even higher.

Only three players in the league have scored more than his 1,439 points this season (DeMar DeRozan - 1,547, Trae Young - 1,475, Giannis Antetokounmpo - 1,443), while only DeRozan (566) and Nikola Jokic (516) have hit more than his 500 field goals.

Interestingly, Tatum took more of a back seat when Boston beat Brooklyn earlier this month, with Brown and Marcus Smart (both 22) scoring more than his 19 points.

KEY BATTLES – Make a better start, Brooklyn

The recent game between these two saw the Celtics race out to a 35-16 lead after the first quarter. It was always a big ask for the Nets to do anything from there.

Where Brooklyn will likely look for success is in mid-range, where no team in the league has a higher percentage of field goals from (48.7). However, only four teams have a lower percentage of mid-range field goals allowed than Boston (39.9 per cent).

HEAD-TO-HEAD

Although the Celtics won at Barclays Center earlier this month, the Nets had won the previous four meetings between the two, including at TD Garden in November, and all three encounters last season.

Alexander Zverev has been "withdrawn" from the singles competition at the Mexican Open in Acapulco after attacking the umpire's chair at the end of his defeat in the doubles.

Zverev and Brazil's Marcelo Melo were in a super tie-break against Lloyd Glasspool and Harri Heliovaara when they were angered by a call made by the umpire.

A return on Melo's serve seemed to be called out by a line judge, but the umpire overruled the decision to put Glasspool and Heliovaara 9-6 up and give them match point, a subsequent ace ending the match in their favour.

As the pairs shook hands at the net afterwards, Zverev quickly walked off and smashed his racquet against the umpire's chair three times.

He then shouted at the umpire that he had "destroyed the whole f****** match" before striking the chair once more.

Zverev was due to face Peter Gojowczyk in the second round of the singles, but the ATP Tour confirmed the Olympic champion has been removed from the draw.

A brief statement read: "Due to unsportsmanlike conduct at the conclusion of his doubles match on Tuesday night, Alexander Zverev has been withdrawn from the tournament in Acapulco."

Rafael Nadal equalled the best start to a season in his career after winning his first match at the Mexican Open on Tuesday.

In his first match since a record 21st grand slam title in Australia, Nadal was a comfortable 6-3 6-2 winner over Denis Kudla, dropping only four points on serve.

Nadal is now 11-0 for the season, equalling the start he made in 2014, when his winning run was ended by Stan Wawrinka in the Australian Open final.

"I think I started playing well, a good victory in straight sets. That's always very positive for the confidence," said Nadal. "I think I played a very solid match for the first day.

"Of course, there are a couple of things that I can do better, but in general terms, I played well, so I can't complain at all."

Daniil Medvedev, who had also not played since the final in Melbourne, came through a tougher contest against Benoit Paire 6-3 6-4 in his opening match in Acapulco.

Medvedev held a two-set lead and looked in control before Nadal came roaring back to claim the Australian Open title, but the Russian could claim a landmark achievement in his first tournament since that heartbreak.

Medvedev, who faces Pablo Andujar next, will become world number one if he wins in Mexico, regardless of Novak Djokovic's performances in Dubai.

"It's always not easy to come back after some rest and some time off competition," he said. "I felt like my sensations were not at the top today, but I managed to fight until the end against a very tough opponent, and I'm happy that I managed to win."

Stefanos Tsitsipas racked up the 200th win of his career, holding off Laslo Djere to win two tie-breaks. He will now face J.J. Wolf, who surprised Lorenzo Sonego by fighting back from a set down to win 3-6 7-6 (9-7) 6-2.

Cameron Norrie was a straight-sets winner over Daniel Altmaier, while Yoshihito Nishioka battled through against veteran Feliciano Lopez.

Tommy Paul progressed after Matteo Berrettini retired when the American was poised to tie the match at one set all. John Millman also had to call an early halt to his match with Marcos Giron after a freak accident on court in which the Australian accidentally hit a ball into his eye.

At the Chile Open, home favourite Alejandro Tabilo beat Renzo Olivo in straight sets, while fifth seed Federico Coria was earlier knocked out by Yannick Hanfmann.

Miomir Kecmanovic defeated Marco Cecchinato, while there were also wins for seeds Sebastian Baez and Facundo Bagnis.

Tiger Woods recently vowed the PGA Tour has not seen the last of him, but surely it has seen the best of him.

This week marks 30 years since a 16-year-old Woods took his first steps onto the professional circuit, the first patter of Tiger feet coming at the Nissan Los Angeles Open, at Riviera Country Club. It is the tournament now known as the Genesis Invitational.

He appeared as an amateur, on an invitation proposed by tournament director Greg McLaughlin, and went up against an elite field on the par-71 course.

Before teeing up with tour pros Bob Friend and Dicky Thompson, however, Woods played the pre-tournament pro-am in the company of Columbo actor Peter Falk. Just one more thing... to make his week memorable.

Woods had been touted for many years as a star in the making, having first caught the eye as a prodigious talent before starting school. He won the U.S. Junior Amateur title in consecutive years from 1991 to 1993 to underline that quality.

And while his first taste of life among the elite was not a triumphant experience, neither did Woods embarrass himself on February 27 and 28, back in 1992. It was clear to many that his talent had not been overstated, and barely five years later this student of the greens and fairways had graduated to become a Masters champion.

Scores of tournament wins have come Woods' way, and there have been storied crises off the course too, most recently with his car crash horror last February 23.

Here, Stats Perform winds back the clock three decades, and reflects on the career of an all-time sporting great.

How did Tiger get on?

By his latter-day standards, awfully. But for a kid, just fine. Woods shot 72-75 to be five over par, and that meant he was 17 shots behind leader Davis Love III through 36 holes.

Love went on to lose in a playoff to Fred Couples for the title, while Woods, who was then the youngest player to appear in a PGA Tour event, missed the cut.

Some 24 years later, Woods would serve as a vice-captain to Love on Ryder Cup duty, but in 1992 they were poles apart.

However, this was a taster for Woods of the life that awaited him, and as much as the cameras were trained on the fabled youngster, he remained a boy in a man's world.

It was said that he had grown from 5ft 6in in 1990 to 6ft 1in by 1992, a spurt that meant his physique was becoming the ideal complement for his natural talent, but the 16-year-old Woods was still somewhat scrawny. Like millions of young American boys across the country, he was within touching distance of adulthood, but still tantalisingly distant.

A crisp three-wood from the first tee set him on the way to a respectable opening round of one over par, before his game dipped slightly on the Friday.

What they said?

According to Sports Illustrated, Woods' father Earl said of his son's performance: "He was playing army golf: left, right, left, right.

"But he was getting up and down like a thief. He recovered and made pars from positions that Riviera hasn't seen in a long time."

Woods was braced for teasing from his fellow students at Western High in Anaheim after failing to make it into the weekend, but those around Woods knew the trajectory of his career was only going upwards.

Mother Kultida still urged expectations to be kept in check, telling the Los Angeles Times on day one of the tournament: "He’s just a kid, just 16. It's hard for people to understand that, because he has the ability. But playing here is just a test for Tiger, to see where he is at and how far he needs to go. Let him be a kid. He loves to play."

Tiger's verdict? 'I'm not ready for this'

"It was a learning experience, and I learned I'm not that good," Woods said after completing his second round. "I can play at the junior level, but I'm not good enough to compete at this level.

"You look up at the board and see 12 under. These guys are just too good. I just don't think I'm ready for this. I have a long way to go."

He also described the experience as "the greatest two days of my life", and in 2018, on his personal website blog, said it had been "very motivating".

"At the time," Woods explained, "I hadn't played amateur golf yet; just junior golf. I skipped the amateur ranks to play in one event. It made me more determined than ever to work on my game and improve."

Here's a fact that still jars with Woods: he has never won at Riviera, where nowadays he is the tournament host.

What became of his playing partners

Neither Friend (72-71) nor Thompson (69-78) made the cut, so it was hardly the most successful grouping of the week.

Friend had his most successful year as a pro in 1998, when he earned the only three top-10 PGA Tour finishes of his career. The highlight was a second place at the Bell Canadian Open, where he lost out to Billy Andrade in a playoff for the title. By that point, Woods was a Masters champion, and he did not compete that week at Glen Abbey.

Thompson had an 11th-place finish at the 1992 Buick Southern Open and signed off his career with just two top-10 results in a PGA Tour career spanning 1991 to 1998.

Both can tell a first-hand anecdote or two about Tiger Woods from that day though.

As Friend said, according to pgatour.com: "The first [reaction] is, 'Oh man, this place is going to be a zoo'. People were all over the place.

"He was very much in his own bubble. We talked about school, 'How do you like school? What's your favourite subject?’.

"It was like playing with any other professional. Some guys talk. Some don't. He wasn't the least bit flummoxed by anything. He was very focused on what he was doing. He had the moxie of a guy who was a senior in college."

What now for Tiger?

As we know, the boy Woods went on to become the dominant golfing man of his generation.

With 15 majors among his record-tying 82 PGA Tour wins, his status as a sporting great is assured.

Woods also has 199 top-10 finishes on tour, and it might be more realistic to expect him to round that up to 200 than to imagine him winning again, as he battles to recover fully from the major leg injuries he sustained in an SUV roll that occurred in this week last year. He was fortunate to escape with his life, police said.

Woods said last week that he could not commit to returning to the PGA Tour in 2022, telling CBS: "You'll see me [again] on the PGA Tour, I just don’t know when.

"Trust me, I'd love to tell you I'll be playing next week but I don't know when, which is frustrating in that sense because I've been down this road too before with my back when I didn't know when I'd come back."

Whether he eventually does come back, or whether this is perhaps the end of the road for Woods the competitor, the world will be waiting and watching.

All those years ago at Riviera, he spoke of having "a long way to go". He went there, and then some.

Emma Raducanu was forced to retire in her first WTA Tour match since the Australian Open.

The US Open champion exited to Danka Kovinic in round two in Melbourne, as her bid for another major title was hampered by a painful blister to her right hand.

A month on, Raducanu took on Daria Saville at the Abierto Zapopan in Guadalajara but was forced to call a halt to proceedings after three hours and 36 minutes, with the scores at 5-7 7-6 (7-4) 4-3. It was the longest WTA match of 2022.

The 19-year-old had fallen at the first hurdle at last year's Linz Open, the only previous event where she appeared as the top seed, and she might have feared a repeat amid a slow start on Tuesday.

Raducanu and Saville traded early breaks, before the Australian seemed to settle first, claiming a 3-1 lead.

Back roared Raducanu and a tense opener continued in back-and-forth fashion, although the big opportunities fell the Briton's way.

She let slip three break points at 5-4 but had four more at 6-5, eventually able to celebrate with a mixture of relief and delight when Saville netted.

Raducanu served for the match at 5-3 in the second, but Saville battled on not only to force the tie-break but also a deciding set.

The Australian fell 2-0 down in the third but was ahead 3-2 when Raducanu took a medical time-out and returned to court with heavy strapping on her leg. After struggling through another two games, Raducanu retired a break down at 4-3, meaning Saville will progress to face Caroline Dolehide.

Meanwhile, after the shock exit of Madison Keys the previous day, Raducanu's fellow seeds had no such issues this time around.

Sara Sorribes Tormo and Camila Osorio each advanced in straight sets, beating Katie Volynets and Viktoriya Tomova respectively.

Zion Williamson's failure to welcome CJ McCollum to the New Orleans Pelicans added to a "pattern of behaviour" that shows the former first overall pick to be "a detached team-mate".

That is the view of JJ Redick, a former Pelicans team-mate.

Injuries have limited Williamson to just 85 games in the NBA since he was drafted in 2019, meaning the discussion around the forward has instead centred on his commitment to the Pelicans.

The team have made moves to try to build a competitive team in the absence of a potential superstar, who averages 25.7 points for his career.

But McCollum, the latest recruit from the Portland Trail Blazers, said at the weekend he was yet to speak with Williamson directly.

And Redick, speaking on Tuesday, was able to offer an insight into life alongside the 21-year-old, whose status remains unclear as he waits to play his first game this season following a foot injury.

"This just shows a complete lack of investment in your team, in the organisation, in the city," Redick told First Take.

"I get that he's hurt and away from the team, but you just traded for one of the 50 best players in the league – a guy that's supposed to be paired with you. Reach out and say, 'hello'.

"This is a pattern of behaviour with Zion that we are seeing again and again. I was his team-mate; I can describe him as a detached team-mate – that is an accurate statement."

Redick, who joined the Pelicans at the same time as Williamson and left in March 2021, said: "Yes, he's been amazing when he's been on the court – 100 per cent.

"He's amazing to watch. There's no one that can do what he does on a basketball court.

"But as a team-mate, there is a pattern of behaviour; as a fully invested individual in New Orleans, there's a pattern of behaviour. This is worrisome."

Phil Mickelson has apologised for his "reckless" comments promoting the possible Saudi Arabia-backed Super Golf League, while he announced he will also take a break from the sport.

A number of high-profile golf stars were reportedly targeted by organisers of a lucrative alternative to the PGA Tour, including Dustin Johnson and Bryson DeChambeau.

But most of the leading names – the likes of Rory McIlroy, Jon Rahm and Collin Morikawa – denounced the league, instead pledging their allegiance to the PGA Tour.

However, Mickelson was a vocal supporter of the new potential competition, claiming it could provide players with "leverage" as a "once-in-a-lifetime opportunity" to "reshape how the PGA Tour operates".

The American golfer went as far as suggesting he and several other golfers paid their lawyers to construct the proposed breakaway competition's agreement, even though he stated Saudi Arabia has "a horrible record on human rights."

Mickelson's comments prompted further backlash from McIlroy, who slated the claims, and the 51-year-old has now apologised for any offence caused by his antics.

In a statement on Tuesday, Mickelson said: "Although it doesn't look this way now given my recent comments, my actions throughout this process have always been with the best interest of golf, my peers, sponsors, and fans.

"There is the problem of off-record comments being shared out of context and without my consent, but the bigger issue is that I used words I sincerely regret that do not reflect my true feelings or intentions. 

"It was reckless, I offended people, and I am deeply sorry for my choice of words. I'm beyond disappointed and will make every effort to self-reflect and learn from this.

"Golf desperately needs change, and real change is always preceded by disruption. I have always known that criticism would come with exploring anything new. 

"I still chose to put myself at the forefront of this to inspire change, taking the hits publicly to do the work behind the scenes.

"Despite my belief that some changes have already been made within the overall discourse, I know I need to be accountable. 

"For the past 31 years, I have lived a very public life and I have strived to live up to my own expectations, be the role model the fans deserve, and be someone that inspires others."

Mickelson also suggested he would take a break from golf to focus on himself.

"I've worked to compete at the highest level, be available to media, represent my sponsors with integrity, engage with volunteers and sign every autograph for my incredible fans," he continued.

"I have experienced many successful and rewarding moments that I will always cherish, but I have often failed myself and others too.

"The past 10 years, I have felt the pressure and stress slowly affecting me at a deeper level. I know I have not been my best and desperately need some time away to prioritise the ones I love most and work on being the man I want to be."

Jannik Sinner saved three match points to avoid a shock defeat to Alejandro Davidovich Fokina in the first round of the Dubai Tennis Championships.

After losing the first set, the world number 10 staved off defeat in a nerve-wracking second-set tie-break.

The fourth seed clung on as Davidovich Fokina saw a trio of opportunities to clinch a shock win go begging, the Spaniard made to pay as his Italian counterpart fought back to prevail 4-6 7-6 (8-6) 6-3.

Sinner, who will next face former world number one Andy Murray, said: "It was a very tough match. I know him, but we've never played against each other.

"It was the first time for both of us and it was a tricky one, saving three match points. On the first one I got lucky because it was out, but not so far [out]."

Second favourite Andrey Rublev won both the singles and doubles titles in Marseille last week and continued his fine form with a 6-4 7-5 win over Daniel Evans that saw the Russian send down 28 winners.

Sixth seed Denis Shapovalov had to recover from a set down to see off Marton Fucsovics, though fifth seed Hubert Hurkacz enjoyed a more routine straight-sets triumph over Alexander Bublik.

Eighth seed Roberto Bautista Agut made relatively light work of Arthur Rinderknech but defending champion and seventh seed Aslan Karatsev was stunned 7-5 6-3 by Mackenzie McDonald.

Karen Khachanov needed a little shy of three hours to beat Alex de Minaur, his dubious reward a second-round clash with Novak Djokovic as the world number one continues his return to the Tour following his controversial Australian Open absence.

Luka Doncic took criticism of his weight at the start of this NBA season to heart and has since been "unstoppable", according to Dallas Mavericks owner Mark Cuban.

For the second season running, Doncic was the preseason MVP favourite; for the second season running, the Mavs superstar was accused of turning up for work out of shape.

Doncic himself acknowledged he "maybe" relaxed "too much" after leading Slovenia in a sensational deep run at the Tokyo Olympics.

The 22-year-old vowed to "trim down" and "do better" and has done exactly that – reportedly now at a similar weight to his rookie year.

The Mavs were 17-18 up until the end of December, with Doncic featuring in only 21 games and averaging 25.6 points, 8.5 assists, 8.0 rebounds and a plus/minus of -4.0.

In 2022, the team are 18-6, carried by their main man's 29.3 points, 9.4 assists and 10.3 rebounds per game, along with a plus/minus of 9.1. He has not missed a game since January 7.

This calendar year, Doncic ranks third for total points (674), second for total assists (217) and sixth for total rebounds (236) – a response, Cuban suggests, to early-season criticism.

"I think he was humbled a little bit," Cuban told The Ticket. "I think he didn't like being called out for his weight and other things, and it finally clicked that there's a level of discipline that's required.

"All athletes at his level go through it at some level, where things are just easy and you're always used to being the best and you're always used to getting all the accolades.

"Then when something doesn't go according to expected, it makes you reconsider.

"He knows what he needs to do, and it finally clicked that if he's going to be the best – and I know he wants to be the best – there's certain things he has to control.

"Once he got a handle on those things, it's just been 'Katie, bar the door'. He's just been unstoppable."

Defending champion Petra Kvitova and former world number one Victoria Azarenka were both forced to withdraw from the WTA Qatar Ladies Open through injury on a day where the top seeds all cruised through in Doha.

Kvitova – who won the 2018 and 2021 editions of the tournament, beating Garbine Muguruza in the final on both occasions – was left unable to continue during her clash with Elise Mertens, later tweeting that an injury to her left wrist had flared up during the second set.

Her conqueror Mertens will face fourth seed and WTA St Petersburg champion Anett Kontaveit in the round of 16 after the Estonian's win over Ana Konjuh on Monday.

Meanwhile, Azarenka joined Kvitova in announcing her withdrawal through injury, suffering pain in her left hip ahead of her scheduled clash with American Madison Brengle.

The tournament's top seeds had more luck on a day of few surprises. World number two Aryna Sabalenka breezed to a 6-2 6-2 victory over France's Alize Cornet, with the Belarusian the favourite for the first WTA 1000 event of the year as world number one Ashleigh Barty is missing through injury.

Elsewhere, world number three Barbora Krejcikova made light work of Poland's Magda Linette, winning 6-1 6-3, and will face former French Open champion Jelena Ostapenko in the round of 16, having eliminated the Latvian from last month's Australian Open.

Paula Badosa also recorded a straight-sets victory, seeing off Clara Tauson 6-1 6-2 to reach the last 16, where she will face 17-year-old American Cori Gauff, who defeated France's Caroline Garcia 6-2 7-6 (7-3).

There were also three-set wins for top-10 players Iga Swiatek and Ons Jabeur, with Swiatek beating Viktorija Golubic 6-2 3-6 6-2, and Jabeur overcoming Aliaksandra Sasnovich 1-6 7-5 6-3.

In the final match of the day, world number six Maria Sakkari downed American Ann Li 6-3 6-3.