Top seed Serena Williams recovered from a slow start to reach the third round of the Australian Open for the 14th time in 15 appearances on Thursday.

Williams, whose sole loss in the second round came on her debut in 1998, had to save three set points when trailing 5-3 in the opening set before reeling off 10 games in a row to beat Vera Zvonareva 7-5 6-0.

"She started out really well, really played aggressive and I was a little too passive," said Williams, who is seeking a 19th grand slam title to edge closer to record holder Steffi Graf, who won 22.

"Once I got down I thought 'You have done so well here, you have nothing to lose, have fun' and I just started to play a lot better. Things really clicked. I had no other option but for things to click. I just had to start playing better."

Zvonareva is currently ranked 203rd in the world but is competing in Melbourne on a special ranking after an injury-plagued 2014 which saw her play just five tournaments.

The 30-year-old Russian, who lost to Williams in the 2010 Wimbledon final, looked certain to take the opening set when she led 5-3 and forced three break points on the American's serve, but Williams saved all three and finally won the game with an ace.

Williams took advantage of her reprieve to break back and powered through the rest of the contest to join elder sister Venus in the last 32.

Williams was reluctant to discuss suggestions of sexism at the Australian Open after a male on-court interviewer sparked outrage by asking some female players to 'give a twirl'.

However, the world number one acknowledged that leading men's players would never be asked to do the same in post-match TV interviews.

Both Williams and Canada's Eugenie Bouchard were asked to spin around to show off their outfits during on-court interviews in Melbourne, prompting an angry response on social media and accusations of sexism levelled at Tennis Australia commentator Ian Cohen, who made the request.

Wimbledon runner-up Bouchard looked slightly bemused by the request, which followed her 6-0 6-3 win over Kiki Bertens, admitting in her post-match press conference the question had taken her by surprise.

"It was very unexpected. I mean, yeah, I don't know. An old guy asking you to twirl, it was funny," said the seventh seed.

Williams, revealed she had also had the same request and not enjoyed the experience, but would not be drawn on whether it was sexist or not.

The American said: "A commentator asked me to twirl. I wouldn't ask Rafa (Nadal) or Roger (Federer) to twirl. Whether it's sexist or not, I don't know. I can't answer that.

"I didn't really want to twirl because I was just like, you know, I don't need all the extra attention."

Venus Williams, who has not gone beyond the third round of any slam since Wimbledon in 2011, defeated compatriot Lauren Davis for the second tournament running.

The Williams sisters withdrew from the doubles in Melbourne, apparently simply to concentrate on the singles, although Venus was rather coy on the subject.

"According to the rules you don't have to give a reason. I think we'll stick with that," she said.

Pressed on whether it was due to the heat in Melbourne, she added: "No further questions on that. I object. Sustained. Thank you."

Venus will play Italy's Camila Giorgi in the third round and is scheduled to meet sixth seed Agnieszka Radwanska in the last 16.

Radwanska appears to be enjoying life with new coach Martina Navratilova as she thrashed Sweden's Johanna Larsson 6-0 6-1 in just 44 minutes.

Fourth seed Petra Kvitova was also a comfortable winner, the Wimbledon champion beating Germany's Mona Barthel 6-2 6-4 to set up a third-round clash with 19-year-old American Madison Keys, who defeated 29th seed Casey Dellacqua.

The much-anticipated clash between eighth seed Caroline Wozniacki and two-time champion Victoria Azarenka (pictured) did not quite live up to the hype, Azarenka edging a tough first set before winning 6-4 6-2 on Margaret Court Arena.

Azarenka is not seeded at a grand slam for the first time since 2007 after a 2014 season hampered by injury and the end of a long-term relationship, but always had the upper hand over fellow former world number one Wozniacki.

The 25-year-old raced into a 3-0 lead and although Wozniacki fought back to get on level terms at 4-4, Azarenka broke serve for the third time in the next game and served out to take the opening set after 58 minutes.

Two more breaks of serve gave Azarenka command of the second set and after fittingly reaching match point with her first ace of the evening, the Belarusian put away a backhand volley to secure victory.