Dominic Thiem ousted World No. 1 Novak Djokovic in a grueling 7-5, 6-7 (10), 7-6 (5) semifinal match at the Nitto ATP Finals on Saturday to reach the tournament final for the second straight year.

Djokovic fought off four match points in the second-set tiebreaker to stay in the match, but Thiem won the third set in dramatic fashion to advance to the final. The nearly three-hour match was remarkably close, with Thiem winning 119 of the 234 points to 115 for Djokovic.

Djokovic held a 4-0 lead in the third-set tiebreaker but Thiem rolled off six straight points. The Serb fought off one match point before World No. 3 Thiem sealed the victory.

Thiem, a 27-year-old Austrian and the winner of the U.S. Open in September, lost the ATP Finals to Stefanos Tsitsipas of Greece in 2019.

"It was for sure a mental battle. I got so tight in the second-set tie-break because to play these legends is always going to be something special," Thiem said in an on-court interview. "Playing for the final here at the Nitto ATP Finals is also something very special and I thought that after my first big title in New York, maybe I'm going to be a little bit more calm, but that was a mistake, I guess.

"I was just as tight and as nervous as before. It was so much on the edge that match, like every single match here. The best players in the world are facing off. So I'm just incredibly happy to be through and just (will) try to get ready for tomorrow."

Djokovic has won five Nitto ATP Finals championships, one away from tying Roger Federer's record of six.

"He did everything right from 0-4 in the third-set tiebreak," he said of Thiem. "I have to put my hats down and say, congratulations. I actually didn't play bad any point after 4-0. I thought (in) every point, I was in it. I did hit the ball, I was not pushing it, but he just smashed it and he just played great."

Thiem will meet the winner of Saturday's second semifinal between Daniil Medvedev and Nadal for the title.