Top seeds sail through in San Diego

The top three seeds spent a combined time of less than three hours on court Thursday as number one Vera Zvonareva led the trio into the quarter-finals of the WTA San Diego Open. The Russian, who claimed a 12th career title last month in Azerbaijan, cruised past compatriot Vera Dushevina 6-3, 6-0 to move into a tournament last eight for the ninth time in 2011. German second seed Andrea Petkovic needed a mere 43 minutes to advance as French opponent Virginie Razzano retired with a shoulder injury while trailing 6-2, 3-0. Third-seeded Agnieszka Radwanska also had to cope with a sore shoulder, but the Pole persevered to crush American teenager Christina McHale 6-1, 6-0. Radwanska, who lost the final last year to Russian Svetlana Kuznetsova, will be playing in her seventh quarter-final of the season on Friday. But she admitted that shoulder pain was starting to worry her. "I played better than in my first match, everything was working. I'm worried about the shoulder. I'll have to get it looked at. "It seems every time I come on the the hardcourt in summer it gives me trouble. It's tough to treat." Radwanska said that despite her runaway victory "my serving was not at 100 percent". "I just hope everything will be OK," she added, well aware that the start of the US Open on August 29 is little more than three weeks away. Fourth-seeded Peng Shuai of China was to take on Italian Sara Errani later Thursday, while fifth-seeded Ana Ivanovic of Serbia eased past Italian Alberta Brianti 6-1, 6-2.