Former champion Serena Williams was an easy third-round winner Thursday at the $740,000 Family Circle Cup tennis event.

The fifth-seeded Williams leveled 17th-seeded Marina Erakovic, of New Zealand, 6-2, 6-2 on the green clay at Family Circle Tennis Center. The American great advanced in 1 hour, 28 minutes without losing her powerful serve on Day 4.

The former world No. 1 Williams titled here in 2008 and was the Family Circle runner-up in 2003.

Upsets came when 14th-seeded Slovenian Polona Hercog popped seven aces in dousing third-seeded Frenchwoman Marion Bartoli 6-4, 1-6, 6-4 and 13th-seeded Nadia Petrova dismissed eighth-seeded fellow Russian Anastasia Pavlyuchenkova 6-1, 6-4. Petrova will face Hercog on Friday.

Ninth-seeded Czech Lucie Safarova reached the round of eight by holding off capable Canadian Aleksandra Wozniak 6-2, 6-7 (4-7), 6-1.

This week's titlist will claim $115,000.