Agnieszka Radwanska of Poland was among the early third-round winners Saturday at the U.S. Open.

The second-seeded Radwanska earned a 6-3, 7-5 victory over former world No. 1 Jelena Jankovic of Serbia. The 2012 Wimbledon runner-up will next face Italy's Roberta Vinci, a 6-2, 7-5 winner over Slovakia's Dominika Cibulkova.

Radwanska struggled with her serve on Saturday, as she was broken four times, but countered with six breaks of the continually disappointing Jankovic. The Serb also committed 37 unforced errors, compared to just 15 for Radwanska.

Jankovic was the 2008 U.S. Open runner-up and was the top-ranked player in the world that summer. She has not come close to that status since. 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.

Third-round play will conclude Saturday with scheduled matches for American Serena Williams, sixth-seeded German Angelique Kerber and another former world No. 1 from Serbia in Ana Ivanovic. Ivanovic opens the night session against American Sloane Stephens.