Serena Williams of the United States returns a shot to Caroline Wozniacki of Denmark at the All England Lawn Tennis Club at Wimbledon, in London, at the 2012 Summer Olympics, Thursday, Aug. 2, 2012. (AP Photo/Mark Humphrey)

Photo by: Mark Humphrey

Serena Williams of the United States returns a shot to Caroline Wozniacki of Denmark at the All England Lawn Tennis Club at Wimbledon, in London, at the 2012 Summer Olympics, Thursday, Aug. 2, 2012. (AP Photo/Mark Humphrey)