World number one Novak Djokovic was crowned champion of this year's ATP World Tour finals last night after Roger Federer withdrew from the title clash due to a back injury. The 33-year old Swiss apologized in person to the crowd at the O2 Arena in London and said that he was not match fit to play the match.This was Djokovic's fourth season ending title and he also became the first man to win three World Tour Finals titles on the trot since Ivan Lendl in the 1980s.