Novak Djokovic battled back from a set down to beat Dominic Thiem 6-7 (10-12) 6-0 6-2 in his opening match of the ATP World Tour Finals at The O2 in London.
Thiem had not taken a set off Djokovic in three previous meetings but ended that run with victory in a closely fought first-set tie break.
However, Djokovic responded by racing through the second set to love and then sealed the win by breaking a demoralised Thiem twice more in the decider.
Shot of the match
Thiem got the upper hand in the first-set tie break with a beautifully executed forehand down the line.
Experts' verdict
Peter Fleming: "You would expect Djokovic to be a little more dominant, but he came through it. We will see him start better in his next match and he is going to build."
Greg Rusedski: "If I look at [Milos] Raonic, he has got to be the favourite to get into the semis with Novak. Thiem I would put on the list as the first guy who is going to be out of this."
The match
Thiem was making his debut at the ATP World Tour Finals but showed little sign of nerves in a fiercely-competitive first set.
Although he made no inroads on the Djokovic serve, he reeled off a series of comfortable holds off his own to take it to a tie break and when he then opened up a 6-2 lead, it appeared he would prevail comfortably.
However, Djokovic saved all three and then three more to take the tie break to 10-10, and it was only at the seventh time of asking that Thiem finally clinched the set.
Djokovic reacted angrily to the setback and sent a ball flying off towards his coaches, Boris Becker and Marian Vajda, who were sat in the crowd.
The outburst seemed to have the desired effect on court, because he broke Thiem in the opening game of the second set and went on to whitewash the Austrian to level up the match.
Thiem managed to hold serve at the start of the decider, but he then surrendered his second service game and was unable to recover.