Angelique Kerber celebrated her 29th birthday with a shaky 6-2 6-7 6-2 win over Carina Witthoeft at the Australian Open yesterday but the world number one will have much to ponder in her title defence once the candles are blown out.

The top seed opened nervously in a three-set grind with unseeded Ukrainian Lesia Tsurenko on Monday and again suffered a meltdown when well on top of 89th-ranked Witthoeft at a breezy Rod Laver Arena.

German Kerber squandered a 2-0 lead as she headed for victory in the second set, then shipped 10 successive points to lose the tiebreak and then her serve in the first game of the deciding set.

But the plucky 21-year-old Witthoeft, who had swung hard at every ball to rattle the champion, suddenly fell away, allowing Kerber to rally and close out the 128-minute tussle.

“I’m trying to play more aggressive. But today I was doing a few more mistakes,” said Kerber, who next plays another left-hander in 58th-ranked Czech Kristyna Pliskova, the twin sister of US Open finalist Karolina.

“I was not finding my rhythm from the first ball,” she added.

“At the end I won, and this is all that counts for me.”

Venus through

Seven-times grand slam champion Venus Williams also advanced to the third round with a 6-3 6-2 win over Stefanie Voegele but conceded she was still troubled by an elbow injury that forced her to pull out of the doubles.

The 13th-seeded, who had been scheduled to team up with sister Serena, was close to tears as she talked about the injury that also saw her skip her only warm-up tournament in Auckland two weeks ago.

Her win over Swiss 26-year-old Voegele was achieved in one hour and 23 minutes and set up a meeting with Duan Yingying.

“I’m managing it,” Venus told reporters of the elbow problem.

“I was really disappointed not to be able to play in New Zealand.

“I was hoping to have the capacity to play both events here, but at this point I just need to be careful and just try to maintain myself.”

Williams is making her 17th appearance at the Australia Open, where she reached the tournament final in 2003.