Image:Novak Djokovic holds the men's singles trophy following Roger Federer's withdrawal from the tournament
Image:Djokovic became the first player since Ivan Lendl in the 1980s to win three consecutive World Tour Finals titles - and his fourth in total
Image:Federer appeared on court to apologise for being unable to compete against Djokovic in the final after suffering a back injury when beating Stan Wawrinka
Image:The announcement was made following the doubles final, with Federer wanting to personally explain his situation to his fans
Image:In his place, Andy Murray stepped in to play an exhibition match against Djokovic
Image:But the world No 1 proved too strong for his British opponent
Image:Eventually winning 8-5
Image:Murray also played in a doubles match with John McEnroe, Tim Henman and Pat Cash to entertain the crowd
Image:Murray and McEnroe played some good tennis as they won 6-2
Image:Earlier Bob (L) and Mike Bryan (2nd L) won the doubles against Croatia's Ivan Dodig (R) and Brazil's Marcelo Melo (2nd R)
Image:Actor Ian McKellen (R) was among the crowd at the O2
Image:Chelsea manager Jose Mourinho was also among the crowd
