NEW YORK, Sept. 2 -- World No. 2 Vera Zvonareva squeezed into the fourth round after a hard fight, while 2006 champion Maria Sharapova suffered a surprising defeat at Flushing Meadow on Friday.

The second-seeded Zvonareva, last year's runner-up to Kim Clijsters, earned a 6-4, 7-5 victory over Spain's Anabel Medina Garrigues.

Italy's Flavia Pennetta took down the third-seeded Sharapova 6-3, 3-6, 6-4.

Sharapova was the runner-up at Wimbledon earlier this summer and was coming off a title in Cincinnati last month.

The 26th-seeded Pennetta will follow her hard-earned upset with a fourth-round match against Peng Shuai of China, who ousted German Julia Goerges 6-4, 7-6 (1).

A two-time winner this year, Zvonareva will next take on Sabine Lisicki of Germany, who earned a 6-0, 6-1 victory over American Irina Falconi.

Monica Niculescu of Romania and Germany's Angelique Kerber were also early winners on Friday.

Niculescu thumped Lucie Safarova of the Czech Republic 6-0, 6-1, and will next face Kerber, who ousted Russia's Alla Kudryavtseva 6-3, 6-1.

In later matches of women's draw, ninth-seeded Samantha Stosur will take up Russia's Nadia Petrova and American Christina McHale, who knocked out eighth-seeded Marion Bartoli in the second round, will challenge Russian Maria Kirilenko.

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