Top-seeded Caroline Wozniacki and second-seeded Jelena Jankovic booked quarter- final berths Thursday at the WTA's Family Circle Cup. Wozniacki, ranked second in the world, survived a sluggish second set to down Switzerland's Patty Schnyder 6-2, 7-5. Her third victory in four matches against Schnyder saw Wozniacki line up a quarter-final clash with sixth-seeded Russian Nadia Petrova, a 6-2, 6-4 winner over Aleksandra Wozniak of Canada. Schnyder, 31 and a regular at this green clay tournament, received strong support from the crowd. 'I'm sure the crowd helped her today,' said Wozniacki, 19. 'She really got pumped up and was believing in herself. It's just important to keep focused on your own game.' Wozniacki is seeking a second title in as many weeks, after a triumph at Ponte Vedera Beach last Sunday. 'I think I played pretty aggressively, especially in the beginning. Second set she - I let her dictate a little more,' Wozniacki said. Serbia's Jankovic advanced with relative ease, downing Russian Evgeniya Rodina 6-3, 6-1. 'I think I played much better today than the first round,' Jankovic said. 'I think I was hitting the ball much better and moved much better as well, so I hope to continue.' Jankovic next faces Daniela Hantuchova of Slovakia. Hantuchova defeated Angelique Kerber of Germany 6-7 (6/8), 7-5, 6-3. China's Peng Shuai advanced with a 7-5, 2-6, 6-2 victory over Russian Elena Vesnina. She will face fourth-seeded Australian Samantha Stosur, who beat Russia Vera Dushevina 6-1, 3-6, 6-1. Vera Zvonareva of Russia beat Alona Bondarenko of Ukraine 6-2, 6-1 to line up a clash with American Melanie Oudin, a 6-4, 6-0 winner over qualifier Christina McHale. 