WHEN it comes to Serena Williams, drama, intrigue and occasionally controversy is never too far away.

On the court yesterday, the world No.1 had to save three set points in the first set before taking her place in round two.

Off the court, she and sister Venus Williams courted more controversy by refusing to explain why they had pulled out of the doubles event for the second time in three years.

"I don't think we have to give a reason," said Williams, who beat former world No.2 Vera Zvonareva 7-5, 6-0, having trailed 5-2 and faced three set points at 3-5. "I think Venus answered that already."

It was a frustrating moment but also classic Williams behaviour as they ducked an issue that probably wouldn't have been a story until they did not give a reason.

Tournament director Craig Tiley told Herald Sport that he'd been told the reason for the withdrawal was that both Serena and Venus wanted to concentrate on their respective singles bids, a perfectly valid reason.

But when asked if that was the reason, the younger Williams sister simply said: "Sure".

If that was indeed the reason, then it seems to be working as both sisters took their place in the third round.

Serena was relieved after getting past Zvonareva, the Russian slowly regaining form after a long time out through injury.

"I'm feeling better every day," she said. "I think in the beginning of the tournament every player feels a little sluggish; at least I do. Now I'm feeling like I'm starting to feel better."

Venus Williams continues to show outstanding form, building on her win in Auckland with a second win here, ousting Lauren Davis 6-2, 6-3.

Serena said the fact that Venus, who has been dealing for several years now with Sjogren's syndrome - an auto-immune disease which causes fatigue and joint pain - is playing so well is driving her on.

"She is playing so well, she's doing so good right now," Serena said. "It makes me look (over) my shoulder and I have to play better and I want to do better.

"I always want to be able to stay ahead as much as I can. So I think that's been, for our whole careers, we've kind of motivated each other. We will hopefully continue to do that."

A sixth Australian Open title for Williams would move her above Chris Evert and Martina Navratilova in the all-time list of grand slam champions.

The trio are tied on 18 and Navratilova, now the coach of Agnieszka Radwanska, will be hoping her new charge can stop Williams and the rest.

Radwanska looked right on song as she crushed Johanna Larsson of Sweden 6-0, 6-1 while Wimbledon champion Petra Kvitova continued her good start to the event with a 6-2, 6-4 victory over Mona Barthel.

And Victoria Azarenka, the 2012 and 2013 champion, finally fully fit again after injury, sent a message that she could be one to watch as she beat US Open runner-up Caroline Wozniacki 6-4, 6-2.