LONDON, ENGLAND - NOVEMBER 19: Novak Djokovic of Serbia celebrates victory in his men's singles match against Tomas Berdych of the Czech Republic during day five of the Barclays ATP World Tour Finals at the O2 Arena on November 19, 2015 in London, England. (Photo by Clive Brunskill/Getty Images)
Getty Images

Getty Images Sport Clive Brunskill