Petra Kvitova of the Czech Republic reacts during a first round match against Misaki Doi, of Japan, at the 2013 U.S. Open tennis tournament Tuesday, Aug. 27, 2013, in New York. (AP Photo/Mike Groll)
Petra Kvitova of the Czech Republic celebrates after beating Ekaterina Makarova of Russia in their Women's singles match at the All England Lawn Tennis Championships in Wimbledon, London, Saturday, June 29, 2013. (AP Photo/Anja Niedringhaus)
Serena Williams of the U.S. celebrates after winning against Czech Republic's Petra Kvitova in their WTA Qatar Ladies Open tennis quarterfinal match in Doha, Qatar, Friday, Feb. 15, 2013. (AP Photo/Osama Faisal)
Serena Williams put away defending Wimbledon champion Petra Kvitova 6-3, 7-5 to set up a semifinal match with Victoria Azarenka on Thursday. (Associated Press)
Serena Williams of the United States reacts winning against Petra Kvitova of the Czech Republic during a quarterfinals match at the All England Lawn Tennis Championships at Wimbledon, England, Tuesday, July 3, 2012. (AP Photo/Anja Niedringhaus)
Serena Williams of the United States follows the ball during a quarterfinals match against Petra Kvitova of the Czech Republic at the All England Lawn Tennis Championships at Wimbledon, England, Tuesday, July 3, 2012. (AP Photo/Anja Niedringhaus)