Rafael Nadal reached the ATP Finals 2020 last four by beating 2019 champion Stefanos Tsitsipas in three sets.
The world number two overcame Tsitsipas 6-4, 4-6, 6-2 in London's O2 Arena.
The 34-year-old had been highly consistent until losing serve to drop the second set, but fought back to dominate the decider.
Here are further details.
The 20-time Grand Slam champion is set to face Russian Daniil Medvedev in the semi-finals.
Medvedev is already guaranteed to win Group Tokyo 1970 with Novak Djokovic and Alexander Zverev contesting the remaining last-four place later on Friday.
Medvedev had stunned Djokovic 6-3, 6-3 earlier to make it to the last four.
Meanwhile, Zverev overcame Diego Schwartzman 6-3, 4-6, 6-3.
Nadal threw light on his game after the victory against Tsitsipas.
"I was playing, I think, a great level of tennis for almost two sets," said Nadal.
"The score was close, but in terms of feeling I felt that I was playing better than him. Then the situation changed. He won that game and then I was starting to suffer with my serve."
Nadal also said that since he found a way to win, he was very happy.
"But it's always a good feeling when you are playing well and you're playing against the best players of the world. You know you're going to be in a tough fight. That's what happened tonight. I was able to find a way to win. Very happy," he said.
Earlier on Thursday, Dominic Thiem, who had already made it to the last four, lost 6-2, 7-5 to Russian Andrey Rublev in a dead rubber. US Open champion Thiem had reached the semi-finals by beating Nadal and Tsitsipas to win Group London 2020.
Love Sports news?
Subscribe to stay updated.