Caroline Wozniacki plays at the U.S. Open tennis tournament in New York September 4, 2010. [Xinhua/Reuters File Photo]

Top-seeded Caroline Wozniacki snapped former champion Maria Sharapova in straight sets on Monday to advance to quarterfinals at the U.S. Open.

Another champion ousted on Monday was Svetlana Kuznetsova as the 11th-seeded Russian became the major casualty at fourth round to Slovak Dominika Cibulkova, 7-5, 7-6 (7-4).

Wozniacki, last year's U.S. Open runner-up to Belgian star Kim Clijsters at Flushing Meadow, took advantage of 36 unforced errors from Sharapova, the 2006 champion, to nail a 6-3, 6-4 victory in a little under two hours.

"Even with those undforced errors, I still had the chances and I was 1 for 8 on breakpoints," said the 23-year-old Sharapova.

"Against someone that's playing really well, playing with a lot of confidence, it's really important to take those chances that you have, the very few that come your way."

To Wozniacki, it's not unforced errors but was pressed. "I felt I was playing well there. I made her do those errors, and I'm really happy to be through and that I won this match," said the 20-year-old Dane.

"My strategy was definitely I knew that I had to be ready for the first ball. I knew she was going to try to attack me from the beginning. I knew she was trying to be aggressive.

"For me it was important to keep as many balls in the court but still try to move her around and try to dictate, as well."

The weakest part of Sharapova's game was undoubtedly her serve, as she gave Wozniacki the only break of the opening set when, from leading 40-30 in the fourth game, she produced three consecutive double-faults.

Sharapova's serve failed her again in the second set when she double-faulted in the seventh game to provide Wozniacki with the only break.

In all, Sharapova double-faulted nine-times.