Defending champion Novak Djokovic has reached the final of the ATP World Tour Finals thanks to a three-set victory over Kei Nishikori.

The world number one was in dominant form during the opening set as two breaks of serve saw him come through 6-1 with just 24 minutes on the clock.

Both players exchanged breaks at the start of the second, but Nishikori was rewarded for his persistence at the baseline late on in the set as he took a 5-3 lead before serving it out 6-3.

However, Djokovic responded in ruthless fashion in the decider, breaking Nishikori three times on his way to sealing the win 6-1 3-6 6-0.