Novak Djokovic advanced to the semifinals while Domenic Thiem put himself in a position to join him as play continued at the ATP World Tour Finals on Tuesday.

In the first match, Thiem defeated Gael Monfils 6-3, 1-6, 6-4 in a match with many twists and turns. The Austrian controlled the first set with consistent baseline power, taking it in just 27 minutes. Then, in an act that has been viewed before, Monfils turned what appeared to be an injury into an advantage as he broke Thiem three times in the second set and quickly evened the match.

Play settled into a more conventional style in the deciding set as the two battled with each strong during service games. But with the Frenchman serving at 4-5, Thiem finally broke serve after three double faults to take the set and the match, his first ever ATP World Tour Finals win.

“I tried to avoid the mistake I did in the first match, to drop a little bit. Didn’t really happen that good,” Thiem said. “But I was trying to stay tough in the third set,” said Thiem.

With the win, he could advance to the semifinals with a win against Milos Raonic on Thursday. Meanwhile, Monfils has been eliminated from any chance to advance and may not play Djokovic due to an injury.

“It was a tough one,” said Monfils. “I think I didn’t play a great match, but I gave everything I had.”

In the nightcap, Djokovic defeated Raonic in an extremely close two-setter, 7-6, 7-6. He appeared to have regained some lost confidence in a first set in which he could not shake the Canadian.  And with each player protecting their serve throughout, the set would conclude with a tiebreak.

There, it was the world no. 2 coming up with the clutch shots in key moments and Raonic could not maximize his potent serve as Djokovic took the tiebreak 8-6.

The Serb’s level of play dropped somewhat in the second set as both players struggled to hold serve. Each broke serve twice and play advanced to another tiebreak. Neither could gain an advantage early in the tiebreaker but with Djokovic trailing 4-5, he would win the final three points to win the set and match.

He assessed his performance afterward, “Well, it was a very close match. I think very few points separated us tonight. It really could have gone either way. I was fortunate to get through the first set tiebreaker. I was down very early in both tiebreaks tonight. But I just managed to stay committed and put pressure on his second serves. I had couple looks on his second serves midway through, towards the end of both tiebreaks, which helped obviously to get into the rally. I knew once I get into the rally, I have a better chance to win the point.”

Djokovic continued, “But I should have done my job earlier, to be honest. I’m not very pleased to drop my serve twice against Milos, especially the second time. I was 4-3, 30-Love, then just four pretty bad unforced errors. Credit to him for really hanging in there, putting pressure, being aggressive, especially from the forehand. But, you know, I think I should have done better there.”

With the result, the veteran remains on a path to regain the world no. 1 spot. However, Andy Murray will certainly have a lot to say about that. He will face Kei Nishikori on Wednesday with a spot in the semifinals potentially on the line.