Novak Djokovic (SRB)(2)action against Milos Raonic (CAN)(4)in their Ivan Lendl Group match during Day Three of the Barclays ATP World Tour Finals 2015 played at The O2 Arena, London on November 15th 2016 (Photo by Kieran Galvin/NurPhoto via Getty Images)

Novak Djokovic (SRB)(2)action against Milos Raonic (CAN)(4)in their  Ivan Lendl Group  match during Day Three  of the Barclays ATP World Tour Finals 2015 played at The O2 Arena, London on November 15th  2016









 (Photo by Kieran Galvin/NurPhoto via Getty Images)