Daniil Medvedev notched 13 aces and rallied from a set down to stun world No. 2 Rafael Nadal 3-6, 7-6 (4), 6-3 on Saturday night in the semifinals of the Nitto ATP Finals in London.
Medvedev will face Dominic Thiem in the championship match on Sunday.
Nadal was serving for the match up 5-4 in the second set.
"I felt really strange until 5-4 for him in the second set, when he was serving for the match," Medvedev said after the match. "It felt like I was doing great shots but there was no link in my game and that was why I was losing.
"He was better in the important moments, I couldn't return in the important moments, I couldn't make a good shot in the important moments. I decided to change some small things. Just being closer, going for it a little bit more," Medvedev said.
Nadal's mishit on a forehand proved to be a pivotal point in that key 10th game of the second set, allowing Medvedev back into the match. The match lasted 2 hours and 35 minutes.
"I think at the beginning of the match, he was better than me," Nadal said. "I was able to save my serves with troubles, but then I played well to have the break and then to close the set.
"In the second, a little bit the same story at the beginning, but at the end of the set I was playing a little bit better than him. And then in the 5-4, I think he played a good game and I didn't. I played a bad game. That's it. But I had a big opportunity. I lost a big opportunity."
Medvedev won 77 percent of his first-serve points.
Earlier on Saturday, Thiem ousted World No. 1 Novak Djokovic in a grueling 7-5, 6-7 (10), 7-6 (5) semifinal match 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."
--Field Level Media