Maria Sharapova and Petra Kvitova were battling in a rematch of this year's Wimbledon final when the Russian star retired from their quarterfinal showdown Thursday at the $2.05 million Pan Pacific Open tennis event.

The fifth-seeded Czech Kvitova was leading the second-seeded Sharapova 4-3 in the opening set when the former world No. 1 from Russia twisted her left ankle while serving in the eighth game. She hobbled over to her chair and quit after talking to her trainer.

"I hit a serve and then landed awkwardly on my left ankle," said the three- time major champion Sharapova. "I felt a sharp pain and next thing I knew I was on the floor. It swelled up immediately and I knew there was no way I could continue."

Sharapova was the Pan Pacific champion in 2005 and 2009.

The 21-year-old Kvitova captured her first career Grand Slam title by beating Sharapova in this past summer's Wimbledon final, 6-3, 6-4.

Kvitova's semifinal opponent on Friday will be fourth-seeded Vera Zvonareva, who handled fellow Russian Maria Kirilenko 6-3, 6-3 on Day 5 on the hardcourts at Ariake Colosseum.

The other semifinal will pit third-seeded Belarusian star Victoria Azarenka against ninth-seeded Pole Agnieszka Radwanska. The Wimbledon semifinalist Azarenka beat seventh-seeded former Wimbledon runner-up Marion Bartoli of France 7-5, 6-0, while Radwanska took care of Estonian Kaia Kanepi 6-2, 7-6 (9-7). Kanepi stunned world No. 1 and defending Pan Pacific titlist Caroline Wozniacki here on Wednesday.

The 2011 champion here will collect $360,000.