Wozniacki cruises, Petrova withdraws in Korea

Top-seeded Caroline Wozniacki was an easy second-round winner Thursday at the Korea Open, while Russian Nadia Petrova was forced to pull out of her match because of a back injury.

Wozniacki rolled to a 6-2, 6-3 victory over French qualifier Caroline Garcia, giving the Dane a quarterfinal matchup with seventh-seeded Klara Zakopalova. The Czech advanced Thursday with a 6-1, 7-6 (8-6) triumph over Slovakia's Magdalena Rybarikova.

Zakopalova is 10-3 lifetime at this event, including a runner-up finish in 2010. She has never beaten Wozniacki in two previous meetings, the last matchup coming in the final of the Copenhagen event in 2010.

Petrova, this week's fourth seed, was scheduled to face Spain's Maria Jose Martinez Sanchez, who now advances to the quarterfinals with the walkover and will face Ekaterina Makarova. The eighth-seeded Russian took out American qualifier Jamie Hampton, 6-3, 7-5.

Sixth-seeded American Varvara Lepchenko thumped Spain's Anabel Medina Garrigues, 6-4, 6-1, to reach her fourth quarterfinal of 2012 and the fifth of her career. She has never won a quarterfinal match, however, and on Friday will take on Austrian Tamira Paszek, who won the final 11 games in her 6-2, 6-0 rout of Korean wild card Lee So-Ra.

Friday's remaining quarterfinal will feature third-seeded Kaia Kanepi of Estonia and Dutchwoman Kiki Bertens, both second-round winners on Wednesday.