Many happy returns for birthday girl Kerber

MELBOURNE: Defending champion Angelique Kerber celebrated her 29th birthday with a gritty win at the Australian Open on Wednesday -- and was rewarded by fans serenading her on centre court.

The top seed beat 89th-ranked fellow German Carina Witthoeft but the round two win was far from gift-wrapped and Kerber had to overcome a second-set stutter before taking it 6-2, 6-7 (3/7), 6-2.

As an impromptu rendition of "Happy Birthday" rang out, Kerber, who will next play Czech Kristyna Pliskova, said she was still getting to grips with being world number one.

"To have this pressure is a privilege. It´s completely new for me, but I´m doing well. I´m just trying to enjoy it," she said.

Kerber joined Venus Williams and Svetlana Kuznetsova in round three as the Grand Slam-winning veterans enjoyed smooth progress in sunny conditions on day three.

In the men´s draw, Japanese fifth seed Kei Nishikori marched into the third round alongside former finalist Jo-Wilfried Tsonga, with both winning in straight sets.

Nishikori was extended to five sets in his first-round win over Andrey Kuznetsov, but he found the going a little easier in his 6-3, 6-4, 6-3 win over Jeremy Chardy.

However, he said he hadn´t completely clicked into gear, complaining of "up and down" form after he was broken three times by the 72nd-ranked Frenchman.

"It was too much up and down, too many service breaks for me, but it´s great to win in straight sets," said Nishikori, who had his serve broken three times by Chardy.

"I am hoping to get my ranking up and I played much better than I did in the first round."

- ´Zero, like zero´ -

Nishikori, who believes he is due a first major win this year, next plays either Lukas Llacko or Dudi Sela, with Tomas Berdych potentially awaiting in the fourth round.

France´s Tsonga, who is seeded 12th and was runner-up to Novak Djokovic in 2008, beat Serbia´s Dusan Lajovic 6-2, 6-2, 6-3 to go through.

In the women´s draw, 36-year-old Williams continued her smooth progress when she beat qualifier Stefanie Voegele 6-3, 6-2 to set up a meeting with China´s Duan Yingying.

"I don´t know anything about her. I have never seen her play. Zero, like zero," Williams said of Duan.

Williams, the oldest player in the women´s draw, pulled out of the doubles competition with her sister Serena as a precaution to rest a sore elbow.

Russia´s Kuznetsova thrashed Australian wildcard Jaimee Fourlis 6-2, 6-1 to set up a third-round clash with 31-year-old Serb Jelena Jankovic.

World number one Andy Murray plays Russia´s 156th-ranked Andrey Rublev for the first time later, as the five-time runner-up sets his sights on finally lifting the trophy.

Roger Federer, 35, has a similar situation heading into his first career match-up with America´s Noah Rubin, the 20-year-old world number 200.