Serena Williams and Agnieszka Radwanska were among the third-round winners Saturday at the U.S. Open.

Williams, a three-time champion at Flushing Meadows, overcame a somewhat slow start in the first set and rolled from there in a 6-4, 6-0 victory over Russia's Ekaterina Makarova.

The second-seeded Radwanska, who lost to Williams in the final at Wimbledon earlier this summer, notched a 6-3, 7-5 triumph against former world No. 1 Jelena Jankovic of Serbia. Radwanska has matched her best result in six previous U.S. Open visits, as she also reached the fourth round in 2007 and 2008.

Next up for the 23-year-old Polish native will be Italy's Roberta Vinci, who advanced Saturday with a 6-2, 7-5 win over Slovakia's Dominika Cibulkova, the No. 13 seed.

"I think she's another tough opponent," said Radwanska about Vinci. "No mistakes at all. A lot of slices, spin, and then suddenly some strong hits. I think against her I think I just have to do everything (well)."

Williams is trying for her 15th career Grand Slam title and second of the year. She won at Wimbledon for a fifth time in July and followed that up with titles at Stanford and the Olympics before dropping a quarterfinal match against Germany's Angelique Kerber in Cincinnati last month.

The fourth-seeded American star was the Open runner-up last year to Samantha Stosur and has not won the title since 2008. She beat Jankovic for that year's championship in New York, and Jankovic -- a budding star at the time -- hasn't really been the same since.

After ascending to the world's top ranking that summer, Jankovic has not come close to that status. In each of the subsequent 16 Grand Slam events, only once has she been past the fourth round -- a semifinal appearance at the 2010 French Open.

Williams, who finished off the second set of her match Saturday in a mere 32 minutes, avenged a loss to Makarova in the fourth round at the Australian Open and will next face Czech Andrea Hlavackova, who rallied to beat 14th-seeded Russian Maria Kirilenko, 5-7, 6-4, 6-4.

"Definitely was motivated (by the loss in Australia)," said Williams. "Knowing that I lost, and it could definitely happen again. Did not want that to happen."

Kerber, the sixth seed, dominated Olga Govortsova, posting a 6-1, 6-2 victory over the Belarus native. Kerber's fourth-round opponent will be Sara Errani. The 10th-seeded Italian needed only 59 minutes to advance with a 6-1, 6-1 pasting of Russian Olga Puchkova.

Serbian Ana Ivanovic and Bulgaria's Tsvetana Pironkova rounded out the winners on Day 6.

The 12th-seeded Ivanovic moved on with a 6-7 (4-7), 6-4, 6-2 win over American Sloane Stephens, while Pironkova outlasted Spaniard Silvia Soler-Espinosa 6-1, 6-7 (3-7), 6-3.

Ivanovic and Pironkova will meet in the fourth round.