Melbourne: Second seed Petra Kvitova exposed her ruthless streak, racing into the fourth round of the Australian Open on Saturday after Russian Maria Kirilenko retired with a strained adductor muscle.   

The 24-year-old Kirilenko had dropped the first set 6-0 in just 34 minutes against the Czech, before retiring after she was broken in the first game of the second on Rod Laver Arena.   

The Wimbledon champion advanced to the last 16 against either former French Open champion Ana Ivanovic or Vania King.   

Kirilenko said she injured the muscle in her left leg in the first game, hampering her movement as Kvitova blasted winners from all angles and had her scampering around the court.   

Kvitova showed no mercy and the Russian was forced to take a timeout after going 5-0 down to have her upper left leg heavily strapped.   

While she returned, Kvitova picked up where she left off serving out to love, capped with three successive aces.   

Kirilenko asked for more strapping between the set changeover and returned to the court, but after Kvitova broke her serve, she felt unable to continue.   

Kvitova said after the 38-minute match that she had been pleased with the way she had stayed mentally focused during the lengthy medical timeout and after Kirilenko returned.   

"What I played (in) the first five games was great," Kvitova, whose Melbourne Park title credentials are firming, told reporters.   

"Sometimes a timeout is very tough, 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.    

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

"I'm really happy how I played today (and) hopefully it will continue like this."