Serena Williams of the United States celebrates scoring during her fourth round match of women's singles against Maria Sharapova of Russia at the 2010 Wimbledon Tennis Championships in London, Britain, June 28, 2010. Williams won 2-0 to enter the quarter-finals. [Xinhua/Zeng Yi]

Defending champion Serena Williams outplayed Russisan ace Maria Sharapova in straight sets on Monday to set up a quarterfinal encounter with China's top female player Li Na at the Wimbledon Championships.

The top seeded American won the tough match 7-6 (11-9), 6-4 while the ninth seed Li defeated Agnieszka Radwanska from Poland 6-3, 6-2.

As China's sole top 10 player in the singles, the 28-year-old Li produced her best Grand Slam result with a semifinal finish at this year's Australian Open. It was the eventual winner Williams who stopped her to go further at Rod Laver.