LONDON: Novak Djokovic survived an early setback, and then made it look all too easy.

The second-ranked Serb, who has a chance to reclaim the No. 1 ranking at the O2 Arena next weekend, rallied to beat Dominic Thiem 6-7 (10), 6-0, 6-2 Sunday in his opening match at the season-ending ATP finals.

Djokovic won nine of 10 games to take control of the match after losing the first set in a tiebreaker. And even that was close.

"Yeah, a thrilling tiebreaker," Djokovic said. "I had, I think, only one set point. He just played a good point. I was in the rally, but he just was going for his shots."

Thiem had his first three set points at 6-3 in the tiebreaker, but he double-faulted twice and then put a backhand into the net to make it 6-6.

Djokovic had a chance, too, leading 9-8. But he couldn't close it out with Thiem serving, eventually hitting a backhand long. The Austrian finally won it on his seventh set point with a forehand winner, prompting Djokovic to smack a ball into the crowd.

After that, it was just about all Djokovic. The Serb reeled off six straight games to send it to a third set, and then broke Thiem twice more to close it out.

"Even though I lost the first set, I thought I didn't do too many things wrong," said Djokovic, who saved the only break point he faced. "It was just the very high quality of his game that prevailed in the first set."

In the following sets, it got to be too much for the Austrian, who was making his debut at the tournament for the top eight players in the world.

"I lost a little bit energy, not much, but just a little bit (after the first set)," Thiem said. "Of course, against a player like Novak, he immediately steps up. That's how the second set went."

Thiem said he had a chance to meet Manchester United manager Jose Mourinho after the match, and the pair chatted briefly. Thiem is a fan of English club Chelsea, a team Mourinho has coached in the past.

In the late match, fourth-seeded Milos Raonic of Canada beat sixth-seeded Gael Monfils of France 6-3, 6-4.

Monfils, who was playing at the ATP finals for the first time, hit a pair of "tweeners" in the match, but it was Raonic that got the breaks — one in each half.

Djokovic lost the No. 1 ranking to Andy Murray last week, but he can earn it right back in London. If either of the two wins the title next Sunday, that one will be assured of the top ranking — as long as Djokovic wins another round-robin match on the way to the final.

If Djokovic does reclaim the No. 1 ranking, he would finish the season at the top for the third season in a row and the fifth time in six years. Murray is trying to end up as the top man for the first time.

With a victory on Sunday, Djokovic can also join Roger Federer as the only players to win the season-ending tournament six times. Federer is not playing in London, sitting out the rest of the season as he continues to recover from knee surgery.

Djokovic has had his own injury problems this season, including pulling out of the China Open with an elbow injury in September. In Sunday's match, he called for a trainer during the first changeover, but it was because he hurt his thumb on the court after reaching for an early shot.

"It was just a nasty cut that I had when I didn't manage to return the serve, the first serve," Djokovic said. "Just kind of caught the surface, then I cut myself. It was bleeding. I just wanted to stop the bleeding."