LONDON, ENGLAND - JUNE 29:  Defending champion Novak Djokovic of Serbia returns a shot in his Gentlemen's Singles first round match against  Philipp Kohlschreiber of Germany during day one of the Wimbledon Lawn Tennis Championships at the All England Lawn Tennis and Croquet Club on June 29, 2015 in London, England.  (Photo by Julian Finney/Getty Images)