Novak Djokovic, from Serbia, hits a backhand shot against Marin Cilic, from Croatia, during a quarterfinals match at the Western & Southern Open tennis tournament, Friday, Aug. 17, 2012, in Mason, Ohio. Djokovic won 6-3, 6-2. (AP Photo/Al Behrman)
Novak Djokovic, from Serbia, hits a backhand shot against Marin Cilic, from Croatia, during a quarterfinals match at the Western & Southern Open tennis tournament, Friday, Aug. 17, 2012, in Mason, Ohio. Djokovic won 6-3, 6-2. (AP Photo/Al Behrman)
Marin Cilic after defeating Sam Querrey in a third-round men's singles match at the All England Lawn Tennis Championships at Wimbledon, England, on Saturday, June 30, 2012. (AP Photo/Kirsty Wigglesworth)
Marin Cilic after defeating Sam Querrey in a third-round men's singles match at the All England Lawn Tennis Championships at Wimbledon, England, on Saturday, June 30, 2012. (AP Photo/Kirsty Wigglesworth)
FILE - In this Jan. 24, 2010, file photo, Juan Martin del Potro of Argentina, waves as he leaves the court after his loss to Marin Cilic of Croatia in a fourth round match at the Australian Open tennis championship in Melbourne, Australia. A person familiar with Juan Martin del Potro's plans tells The Associated Press that the 2009 U.S. Open champion will not defend his title at the year's last Grand Slam tournament. The person spoke to the AP on Saturday, Aug. 21, 2010, on condition of anonymity because an official announcement has not been made. (AP Photo/Andy Wong, File)
