Serena Williams and Agnieszka Radwanska posted second-round victories at the 2012 U.S. Open on Thursday.

The former No. 1 Williams, a three-time champ and two-time U.S. Open runner- up, had no problems in a matchup with Maria Jose Martinez Sanchez of Spain 6-2, 6-4.

Williams, the fourth seed, was last year's U.S. Open runner-up to Australian Sam Stosur. She is the reigning Wimbledon and Olympic champion.

The second-seeded Radwanska dropped the first set before coming back to blitz Spaniard Carla Suarez Navarro 4-6, 6-3, 6-0 on the Grandstand court.

The quiet Radwanska, who has a chance to leave the U.S. Open as the top-ranked woman in the world, leads the WTA in Grand Slam match wins this year with 14. She finished runner-up to Williams at Wimbledon this year.

Up next for Radwanska will be former world No. 1 Serb Jelena Jankovic, the 30th seed who handled Spaniard Lara Arruabarrena-Vecino 6-4, 6-2 on Day 4. Jankovic was the U.S. Open runner-up in 2008.

Another former world No. 1 from Serbia, Ana Ivanovic, was an easy second-round winner Thursday. The 12th seed blew past Swedish veteran Sofia Arvidsson 6-2, 6-2 in 64 minutes at Ashe Stadium.

"I'm very happy about today's match, because she's a tough opponent," Ivanovic said.

The 24-year-old Ivanovic is a three-time Grand Slam finalist and captured Roland Garros in 2008.

Meanwhile, 13th-seeded diminutive Slovak Dominika Cibulkova snuck past capable Serb Bojana Jovanovski 7-6 (7-3), 7-6 (7-3), 14th-seeded Russian Maria Kirilenko cruised past Hungarian Greta Arn 6-3, 6-2, and 20th-seeded Italian Roberta Vinci saved a match point before edging Kazakhstan's Yaroslava Shvedova 3-6, 7-5, 7-5. The Olympic bronze medal runner-up Kirilenko was last week's New Haven runner-up to Czech star Petra Kvitova.

American Sloane Stephens beat German Tatjana Malek 5-7, 6-4, 6-2.

Other second-round winners were Bulgarian Tsvetana Pironkova, Russian Ekaterina Makarova, Spaniard Silvia Soler-Espinosa and Czech Andrea Hlavackova.