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With the 62 64 triumph, Lepchenko matched her career-best result - a quarterfinal appearance at Ponte Vedra Beach in 2010. Not only that, but she is the only American still alive at an event that began with eight of them.
"I played great. I was really aggressive and I used all my weapons," Lepchenko said. "With every match, I'm playing better and better."
Joining Lepchenko in the quarters were fourth-seeded Marina Erakovic, Vera Dushevina and Michaella Krajicek, who rallied from a two-break, 4-1 deficit in the first set of her 76(2) 63 defeat of Olga Govortsova.
The first round also wrapped up, with No.2 seed Ksenia Pervak and No.5 seed Pauline Parmentier among those advancing. Pervak was a 62 64 winner over last year's runner-up here, Rebecca Marino, and Parmentier got past Andrea Hlavackova, 64 46 62, in the day's only three-setter.
"She is a tough opponent, especially on fast surfaces like indoors. Last time we played she beat me, so I'm really happy that I'm through," said Pervak referring to her meeting with Marino in the first round of the 2010 US Open. "I think everything was pretty good. I played pretty good from the baseline. My serve was really good. Everything was going my way."