Shahar Peer of Israel captured a third-set tiebreaker 7-5 to defeat 13th-seeded Nicole Vaidisova of the Czech Republic 6-4 3-6 7-6 and advance to the fourth round of the US Open on Saturday.
Peer, a quarter-finalist at the Australian Open, advanced to a round-of-16 match against 18-year-old Agnieszka Radwanska of Poland, who had earlier in the day upset second-seeded holder Maria Sharapova of Russia.
Peer, the 18th seed, prevailed on her fourth match point, benefiting from a fourth forehand error in the decider from the 18-year-old Czech in the first women's match so far to be decided by a third-set tiebreaker.
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The Israeli struck just 22 winners and served only one ace but made Vaidisova work hard with her great defensive play from the baseline.
Vaidisova was playing her first tournament since Wimbledon after being diagnosed with mononucleosis.
"My consolation is I didn't play tennis for two months," Vaidisova told reporters. "And to play such a tough match in such a great atmosphere, I'm just happy with my performance."
The Czech said she suffered from a lack of tournament play, but gave the 20-year-old Peer credit for earning the victory.
"She's such a great defender. She gets so many balls back, more balls than the other girls would," the Czech said.