LONDON (AP) -- Two-time defending champion Novak Djokovic overcame a lapse of concentration to beat Kei Nishikori 6-1, 3-6, 6-0 and advance to a third straight final at the ATP Finals on Saturday.
The Serb, who sealed the year-end No. 1 spot after finishing unbeaten in the round robin phase, dropped his first set since the start of the tournament after losing his focus early in the second set, visibly angered by a partisan crowd.
The fourth-seeded Nishikori failed to build on the momentum at the start of the decider when he missed two break points before Djokovic recovered and won the last six games.
Djokovic, who is bidding to become the first player since Ivan Lendl from 1985-87 to win the season finale three years in a row, will next face either Roger Federer.
''Kei was playing great and this has been the best season of his life, but he made some crucial double faults in the third set,'' Djokovic said. ''Of course I will watch the semi-final. I'll get some popcorn and enjoy it from my bed.''
Djokovic dictated play from the baseline in the first set and broke immediately at the start of the second as he looked poised for another easy win. But his game dropped off suddenly when he let the Japanese newcomer came back with a double fault that the crowd applauded.
Djokovic applauded in return with irony and shook his head in disbelief as he prepared to return Nishikori's next service game. Challenged for the first time this week, the top-ranked Serb could not channel his anger and struggled to recover as he hit just 3 winners to 8 unforced errors in the second set, with Nishikori playing with more confidence and hitting the lines.
After receiving treatment on his right wrist, the U.S. Open runner-up broke for a 5-3 lead following a spectacular point. After a sharp forehand attack, Nishikori dragged Djokovic to the net with a drop shot, before hitting a lob that offered him the chance to conclude with a crosscourt forehand winner, sending the crowd into rapture.
The turning point came in the first game of the third set, when Djokovic - who had lost just nine games in his four previous matches - faced two break points at 15-40. Nishikori, who upest Djokovic in the U.S. Open semifinals, could not seize his chance, hitting two consecutive unforced errors as the momentum swing the Serb's way. Djokovic showed no mercy afterward, extending his indoor unbeaten run to 31 matches.