Sofia Kenin admitted she was given a stern test by Kirsten Flipkens before the Belgian was forced to abandon their tussle at the Abu Dhabi Women's Tennis Open.

With a month to go before Kenin begins the defence of her Australian Open title, the American world number four was fighting to avoid a second-round exit to an experienced opponent.

Flipkens took the first set 7-5 and trailed 5-4 in the second, a break down, when an injury to her left ankle caused her to retire from the match.

A run of three consecutive games and 12 unanswered points from Flipkens had seen the 34-year-old former Wimbledon semi-finalist snatch the opener.

Kenin was turning the contest around in the second set and the top seed admitted she was "a little bit upset" to see Flipkens suffer when injury struck.

"We're good friends and that's not something you like to see," Kenin said, quoted on the WTA website. "I just hope [Flipkens] can have a speedy recovery and get ready for Australia.

"She played a really good match. It was the third time we’ve played each other, and it was a really solid match from both of us. This is not the way I wanted to win."

Aryna Sabalenka could be a player to fear at Melbourne Park in February, as the world number 10 made it 11 consecutive match wins by fending off Australian Ajla Tomljanovic 7-5 6-4.

Sabalenka finished off the 2020 season with titles in Ostrava and Linz so the Belarusian is looking for a hat-trick of tournament triumphs.

Tunisian Ons Jabeur scored a 5-7 6-3 6-2 victory against Kateryna Bondarenko of Ukraine to reach the last-16 stage, and she faces Sabalenka next.

Jabeur won on the only previous occasion she and Sabalenka have met, securing a three-set win in round three of the delayed 2020 French Open.

Alexander Zverev insists his latest split from a high-profile coach ended on amicable terms after David Ferrer cut ties with the US Open finalist.

Spaniard Ferrer's decision to walk away leaves Zverev yet again, now at the age of 23, looking for a coach with whom he might establish a long-term partnership.

The German ditched former world number one Juan Carlos Ferrero in early 2018, after six months together, claiming the coach had been "very disrespectful" to other members of his team.

He then linked up with Ivan Lendl in August 2018 but that lasted just under a year, with Zverev reportedly criticising the eight-time grand slam winner's focus.

This time, Zverev and former world number three Ferrer have not hinted at any animosity or disagreements.

They teamed up in July 2020, and Zverev said of their break-up: "I would like to thank David for the months we have shared, the times on and off the court, wishing him only the best in the future.

"I also want to thank his family for giving me the chance to spend precious weeks with David during these difficult times. I have tremendous respect for the way David played and coaches tennis."

Ferrer helped Zverev battle through to the US Open final in September, where he led by two sets but was ultimately beaten by Dominic Thiem.

Zverev also won a pair of titles in Cologne in October and reached the final of the Masters 1000 event in Paris.

But they are going their separate ways as the new season begins, with the Australian Open just weeks away.

Ferrer said: "At the end of the year, a decision had to be made, I spoke with Sascha [Zverev] and told him that I preferred not to continue, that we were not going to continue next season. Not for anything special, I just didn't think it was time."

Speaking to tennis website Punto de Break, Ferrer added: "Absolutely nothing has happened between us, everything is still fine, in fact I am very grateful to him for the opportunity he gave me to travel with him during that stretch of the season.

"During those months we had a good coexistence, everything was perfect."

Dayana Yastremska says she is "astonished" after the world number 29 was provisionally suspended for failing an out-of-competition doping test.

The International Tennis Federation (ITF) on Thursday revealed Yastremska was charged on December 22, having tested positive for mesterolone metabolite in a sample taken on November 24.

Ukrainian Yastremska, who reached a career-high 21st in the rankings 12 months ago, says she is not guilty of any wrongdoing and will do all in her powers to clear her name.

The 20-year-old posted on Twitter: "I firmly state that I have never used any performance-enhancing drugs or any prohibited substances.

"I am astonished and under shock, particularly given that two weeks prior to this test - on 9 November 2020 - I tested negative at the WTA event in Linz. After this last tournament of the year, I stopped practising to rest prior to the start of the new season.

"Only a very low concentration of mesterolone metabolite was detected in my urine. Given that low concentration and given my negative test two weeks earlier, I have received scientific advice that the result is consistent with some form of contamination event.

"Besides, I have been informed that this substance is meant for use as medication by men and that women are advised not to use it due to the adverse effects it causes."

Yastremska said she was "resolutely determined to do everything to clear my name".

Rising star Yastremska has three WTA singles titles to her name.

Sofia Kenin and Coco Gauff both made it through to the second round of the Abu Dhabi Women's Tennis Open on a day of few shocks. 

Seven of the nine seeds in action on Thursday advanced, with only Marketa Vondrousova and Jennifer Brady falling by the wayside. 

Those upsets came despite Vondrousova and Brady each winning their opening sets - against Hsieh Su-wei and Tamara Zidansek respectively - the latter racing through 6-0 in the first before being reeled back in. 

Kenin and Gauff had no such problems, however. 

But top seed Kenin - the 2020 WTA Player of the Year - had to stay patient as she took down 789th-ranked Yang Zhaoxuan 7-6 (7-4) 6-2. 

The first set lasted more than an hour and saw Kenin face five break points, defending each of them, with another 11 Yang opportunities following in the second, although the world number four proved more clinical en route to victory. 

"It was the first match, obviously a bit of nerves, I had to find my groove," Kenin said afterwards. "Conditions weren't easy, it was quite windy.

"The first set was tough for me. I couldn't find the ball, I guess." 

Gauff was comfortable throughout, meanwhile, swatting aside Ulrikke Eikeri 6-0 6-1 to tee up a meeting with Maria Sakkari. 

Elina Svitolina, Karolina Pliskova and Aryna Sabalenka each also progressed in two sets, as did Garbine Muguruza, overcoming a potentially tricky hurdle in the form of Kristina Mladenovic. 

Muguruza was a 6-2 6-4 winner and afterwards said: "I was trying to do my game, dominating, not letting her dominate the point. 

"It's the first match of the year, it's a little bit tricky to get the feeling, but I'm happy with the win." 

Roger Federer decided to miss the Australian Open because wife Mirka opposed having to spend a full fortnight in quarantine, a leading official has claimed.

It was widely assumed Federer's reason for skipping the upcoming grand slam related to the knee surgery he underwent last season.

He had hinted as much, and agent Tony Godsick referred to the knee rehabilitation when announcing in December that the Swiss great would not travel to Melbourne.

But Andre Sa, the head of player liaison at Tennis Australia, says Federer pulled out when it became apparent his wife and children would be holed up in their hotel accommodation for two weeks.

The players travelling to Australia must all quarantine to avoid any possible spread of COVID-19, but they are allocated five hours per day in which they can leave their rooms to train and practise with specified hitting partners.

Sa, a former top-20 doubles player, told Band Sports in his native Brazil that he discussed with father-of-four Federer the practicalities before the 20-time grand slam winner reached his decision.

"The main reason was the quarantine," said Sa. "I talked to him a month ago and he had two options. He could come with the whole family and do the quarantine.

"The problem is that Mirka and her children couldn't leave the room. They would have to stay 14 days in the room. The exception is only for players.

"He could go out, train and come back, but the family couldn't. Mirka did not approve the idea.

"The other option would be for him to come alone. Only there would be at least five weeks away from family and children. And then he said, 'Dude, 39, four kids, 20 grand slams. I'm no longer at the stage to be away from my family for five weeks.'"

Former world number one Federer has not played a tournament since losing to Novak Djokovic in the semi-finals of the Australian Open last year.

This year's edition of the grand slam has been delayed by three weeks to a February 8 start, due to factors tied into the pandemic.

Russell Westbrook, Doc Rivers and Billie Jean King reacted with revulsion to the assault on the US Capitol by supporters of outgoing president Donald Trump, united in the view there would have been a deadlier outcome had the rioters been black people.

On a dark day for the United States, thousands of Trump backers descended on Washington for a protest rally, refusing to accept the result of November's election that saw Joe Biden sweep to power.

Two weeks out from Biden's inauguration, many violent protesters breached security and accessed the Capitol, causing carnage and destruction as they appeared to go largely unchallenged.

There were a number of casualties, with four dead including a woman who was shot, while reports said a number of explosive devices were discovered.

Washington Wizards star Westbrook said: "It's very unfortunate to see. If those roles were reversed, if those were African-Americans, black people, it would be totally different."

He said the chaos was "just crazy, almost like a movie", and team-mate Bradley Beal agreed it was hard to stomach the scenes, given his view that police took a far less lenient approach to protesters during last year's Black Lives Matter demonstrations.

"It's very disheartening in a lot of ways - a lack of sense of urgency to respond to what was going on, versus protesters at Black Lives Matter over the summer," Beal said.

"The people who were invading our Capitol, that's unheard of and it's disheartening this is where we're at as a country."

Veteran Philadelphia 76ers coach Rivers called the insurgency "pretty disturbing" but vowed that "democracy will prevail".

"It shows a lot, though," Rivers said. "When you saw the [Black Lives Matter] protests in the summer, you saw the riots or more the police and the national guard and the army. And then you see this and you saw nothing.

"It basically proves the point about a privileged life in a lot of ways. I'll say it because I don’t think a lot of people want to: could you imagine today if those were all black people storming the Capitol and what would have happened?

"So that to me is a picture that’s worth a thousand words for all of us to see and probably something for us to reckon with again."

Tennis great King, a long-time activist for equality in sport and society, added on Twitter: "If the rioters storming the Capitol building today were Black and Brown people, the police response would be much different."

Footballer Megan Rapinoe became embroiled in a war of words with Trump during USA's triumph at the 2019 Women's World Cup.

Looking at footage of how seemingly easily the protesters were able to break into the Capitol, Rapinoe offered her opinion, writing: "This is crazy, how did they even get through the..... ohhhhh it was opened for them."

Trump had addressed the crowds earlier in the day, forcefully standing by his view that he was fraudulently robbed of an election win.

In the hours after the Capitol was cleared, Congress confirmed Biden's victory.

Richard Sherman, the San Francisco 49ers cornerback, described the rioters as "terrorists".

He wrote on Twitter: "Never thought Americans would let terrorists into the capital without a fight....sad day. There are certain things my brain could never imagine.... and one of them is black ppl storming a government building and taking things without deadly consequences. But that’s just my brain."

It was not just Sherman's brain thinking along those lines, though. Far from it.

Los Angeles Clippers star Kawhi Leonard took the same stance, saying: "You just see the privilege, the privilege in America. "It's sad to see, because if any of us was out there, I think we would've been tear-gassed, Maced, probably gunshots, you know?"

And American track and field legend Michael Johnson said the scenes were only to be expected, given the nature of the Trump presidency.

"The alarms were sounded for four years. Republicans ignored them. Many in the media ignored them and normalized dangerous behavior," Johnson wrote on Twitter.

"Sadly, today it all came to be. Shameful! This president and his supporters. Shame on you! And take responsibility!

"People on Twitter (of course) literally equating BLM protesters fighting for justice and equality to White Supremacist Trump supporters (supposed Patriots) gleefully and violently desecrating America's oldest and greatest institutions of democracy. Sadly, this is typical America."

Veronika Kudermetova started the new season in style by beating 10th seed Anett Kontaveit in the first round of the Abu Dhabi Women's Tennis Open on Wednesday.

Kudermetova had won her only two previous singles matches against Kontaveit and maintained that perfect record with a 7-5 6-1 victory.

The world number 46 from Russia broke four times to seal her place in the second round, with Kontaveit winning just 48.4 per cent of points on her first serve in a rusty beginning to the 2021 campaign.

Donna Vekic was another seed to fall at the first hurdle as Bernarda Pera consigned the Croatian to a 7-6 (12-10) 2-6 6-4 defeat at Zayed Sports City International Tennis Centre.

Kirsten Flipkens could face top seed Sofia Kenin in the second round after defeating Laura Siegemund 5-7 7-5 6-4.

Ons Jabeur is aiming to break into the top 10 this year and the 15th seed got up and running for the season by seeing off Anastasia Pavlyuchenkova 7-6 (7-3) 6-3.

Daria Kasatkina, Yulia Putintseva and Ajla Tomljanovic were among the other players who advanced to round two.