Vera Zvonareva was among the early women's winners in third-round play Friday at the U.S. Open, while 2006 champion Maria Sharapova suffered a surprising defeat.

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 to open play at Arthur Ashe Stadium.

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 (7-1) on Friday.

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. Zvonareva has had a fairly strong summer after a third-round exit at Wimbledon, winning in Baku with a runner-up finish in her next event at Carlsbad and a semifinal appearance at the U.S. Open tuneup in Cincinnati. She was also a third-round loser in Toronto.

Monica Niculescu of Romania and Germany's Angelique Kerber were also early winners on Friday at Flushing Meadows. Niculescu thumped Lucie Safarova of the Czech Republic 6-0, 6-1, and will next face Kerber, a 6-3, 6-1 winner over Russia's Alla Kudryavtseva.

Other third-round matches Friday include ninth-seeded Samantha Stosur against Russia's Nadia Petrova and American Christina McHale against Russian Maria Kirilenko in the opening night match at Ashe Stadium. McHale knocked out eighth-seeded Marion Bartoli in the second round.