Sharapova into Australian Open fourth round

Former champion Maria Sharapova of Russia defeated Germany's Angelique Kerber in straight sets to reach the fourth round of the Australian Open on Saturday.

Sharapova won 6-1, 6-2 in a scoreline that flattered the fourth seed, who was pushed hard by Kerber in the second set.

Wimbledon champion Petra Kvitova benefited from the second injury retirement in quick succession in the women's draw when Maria Kirilenko pulled out of their third round match on Saturday.

The Czech second seed was leading 6-0, 1-0 when Kirilenko, who hurt her thigh towards the end of the first set and needed medical treatment, decided not to continue.

It was the second withdrawal in a matter of hours in the women's third round after Anabel Medina Garrigues pulled out in tears late on Friday after painfully rolling her ankle while playing Chinese fifth seed Li Na.

Kvitova, who will now play either Serbian Ana Ivanovic or Vania King of the United States in the fourth round, had been in scintillating form until Kirilenko's retirement.

She said once she realised her opponent was injured she knew she had to maintain her composure.

"Actually, I just said to myself that I have to play still the same way as before and go for the balls and don't make many mistakes and just be focused," Kvitova said.

"Because sometimes a time-out is very tough for us, because when you are playing really well and then you have five minutes off, sometimes it's tough to get back and play as before."

After breaking Kirilenko's serve in a 10-minute opening game, the Czech world number two raced through the remainder of the set with a succession of booming serves and punishing ground strokes.

Kvitova landed 71 per cent of her first serves and won 90 percent of those points, conceding only two points on her serve in the truncated match.

She also blasted 23 winners past the hapless Kirilenko, who was often left stranded on the baseline.

The Russian left the court for a medical time-out when she went down 5-0, but after losing the next two games she walked to the net to concede the match.

Kvitova's form was a big improvement from her second round match, when she lost the second set to Carla Suarez Navarro and was in trouble in the third before recovering.

"The way I played in the first five games was great," she said. "I mean from the last match that I played it was really a big difference and I'm really happy how I played today. Hopefully it will continue like this."

Kvitova is one of four players who could be world number one at the end of the tournament, along with Victoria Azarenka, Maria Sharapova and the current incumbent, Caroline Wozniacki of Denmark.

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