Serbia's Novak Djokovic returns against Germany's Philipp Kohlschreiber in their fourth round match at the French Open tennis tournament, at Roland Garros stadium in Paris, Monday June 3, 2013. (AP Photo/Michel Spingler)

Photo by: Michel Spingler

Serbia's Novak Djokovic returns against Germany's Philipp Kohlschreiber in their fourth round match at the French Open tennis tournament, at Roland Garros stadium in Paris, Monday June 3, 2013. (AP Photo/Michel Spingler)