Svetlana Kuznetsova of Russia hits a return to Dominika Cibulkova of Slovakia during the U.S. Open tennis tournament in New York, September 6, 2010. [Xinhua/Reuters Photo]

Sharapova was 2-0 lifetime against the 20-year-old Dane, with both matches coming in 2008.

"I felt like I played a couple of good points and then make an easy error, hit a return long or miss a first serve, give her many looks at second-serve returns," said Sharapova.

"I think it just needs to be more stable and not so up and down, especially against an opponent like her.

"I need to string a few more things together than I did. It's all really capitalizing on what you have. You work hard for something, and then you let it slip away. I think I've just got to capitalize on that."

Wozniacki has won 12 straight and 18 of her last 19 matches, including titles in her last two events, in Montreal and New Haven.

Cibulkova dismissed Kuznetsova in two hours, six minutes, as the erratic Russian piled up 10 double faults and had her serve broken on four occasions.

"I would say it was a good match from my side," Cibulkova said. "You know, I was just trying to be aggressive as I could, and Svetlana today, she lets me be more aggressive."

The two-time Grand Slam event champion Kuznetsova titled here in 2004 and was the U.S. Open runner-up in 2007. She hasn't reached the quarterfinals in Flushing since 2007.

The 21-year-old Cibulkova will appear in her second career and first-ever U.S. Open quarterfinal.

Rising 31st-seeded Estonian Kaia Kanepi reached her second straight Grand Slam quarterfinal, as she upended 15th-seeded Belgian Yanina Wickmayer, the 2009 semifinalist here, 0-6, 7-6 (7-2), 6-1.

Kanepi reached her first-ever major quarterfinal at Wimbledon in July.