Kvitova ousts Azarenka as Sharapova pulls out in St Petersburg

Defending champion Petra Kvitova reaches the quarter-finals of St Petersburg Ladies Trophy

Saint Petersburg, January 31: Petra Kvitova knocked out Victoria Azarenka to reach the quarter-finals at the St Petersburg Ladies Trophy - but Maria Sharapova's involvement in the tournament is over after she pulled out due to injury.

Defending champion Kvitova looked on course for a straightforward triumph when she led 6-2 5-1 against the former world number one on Wednesday (January 30).

However, Azarenka battled back impressively in the second set, aided by her opponent sending down a double fault on her first match point, winning four games on the spin to quickly draw level.

A tie-breaker was eventually needed to decide the outcome, with Kvitova - back in action for the first time since losing to Naomi Osaka in the Australian Open final - reeling off five successive points to seize control.

The top seed eventually won 6-2 7-6 (7-3) after one hour and 40 minutes on court, meaning she now leads the head-to-head record 5-3.

Kvitova's quest to retain her crown continues with a clash with Donna Vekic on Friday, the eighth seed progressing thanks to a 6-4 6-3 result against Russia's Veronika Kudermetova.

Sharapova, meanwhile, was forced to withdraw from her match against fellow Russian Daria Kasatkina due to a problem with her right shoulder.

"I tried to do everything possible to be able to be ready to compete this week, but my right shoulder continues to be an issue for me," Sharapova told the WTA Tour website.

"I will meet with my team of doctors over the next few days to evaluate the situation, and I look forward to returning to completion as soon as possible.

"It was so special to play in front of my home crowd this week and I wish I could have continued competing in this fantastic tournament.”

The injury setback for the five-time grand slam winner means Kasatkina - who lost in the opening round at the Australian Open to Timea Bacsinszky - will next face compatriot Vera Zvonareva, who rallied from a set down to beat Julia Goerges 4-6 6-4 6-4, guaranteeing there will be one at least one Russian player in the semi-finals.