Novak Djokovic beat Kei Nishikori 6-1 3-6 6-0 to win a topsy-turvy World Tour Finals semi-final at the O2 Arena in London.
Djokovic, who has been confirmed as the world number one for the end of the year, needed around an hour and a half to overcome the Japanese, who set pulses racing by winning the second set but collapsed to a bagel in the decider, which ended on a double fault.
The Serb will face Roger Federer or Stanislas Wawrinka in the final on Sunday.