Last week's Madrid titlist Serena Williams moved on, while world No. 3 Agnieszka Radwanska and former No. 1 Caroline Wozniacki went by way of the upset Wednesday at the $2.168 million Italian Open tennis event, a clay-court French Open tune-up.

The ninth-seeded former No. 1 Williams had to come from behind to best former top-10 Russian Nadia Petrova 4-6, 6-2, 6-3 in 2 hours, 9 minutes on the red clay at Foro Italico.

The 2002 Rome champion Williams, now 15-0 on clay this year, upset current world No. 1 Victoria Azarenka in last week's finale on the controversial blue clay in Madrid.

Up next for the powerful American will be Spaniard Anabel Medina Garrigues.

Meanwhile, Radwanska succumbed to Czech Petra Cetkovska 6-4, 4-6, 6-1 and the sixth-seeded Wozniacki gave way to the clay-court specialist Medina Garrigues 6-4, 4-0, as the Danish star retired because of upper respiratory illness.

Fifth-seeded U.S. Open champion Samantha Stosur avoided an upset by handling Italian crowd favorite Sara Errani 6-3, 7-5. Stosur was last year's Italian Open runner-up to former No. 1 Maria Sharapova.

Eighth-seeded reigning French Open champion Li Na, of China, got past Czech veteran Iveta Benesova 6-1, 7-5, while another upset came when capable German Julia Goerges drubbed seventh-seeded Frenchwoman Marion Bartoli 6-3, 6-1.

In other second-round action involving seeds, No. 12 German Angelique Kerber whipped American Vania King 6-3, 6-2, No. 13 Ana Ivanovic pasted Spanish qualifier Silvia Soler-Espinosa 6-1, 6-2, and No. 14 Slovak Dominika Cibulkova edged out Italian wild card Karin Knapp 6-3, 4-6, 6-1. Up next for the former French Open champion Ivanovic will be her fellow former No. 1 Sharapova.

South African Chanelle Scheepers overcame New Zealand's Marina Erakovic 5-7, 6-1, 6-2, while Italian favorite Flavia Pennetta dismissed American qualifier Sloane Stephens 6-2, 6-3, and Romanian Sorana Cirstea leveled Swede Sofia Arvidsson 6-3, 6-1 in some other second-round play.

The 2012 Rome titlist will collect $385,000.