Rafael Nadal will face Daniil Medvedev in the semi-finals of the Nitto ATP Finals after ending the title defence of Stefanos Tsitsipas at The O2.
It was a winner-takes-all clash after both men lost to Dominic Thiem but Nadal was upbeat about his level following his narrow defeat by the Austrian on Tuesday, showing here that his optimism was justified with a 6-4 4-6 6-2 victory.
Nadal served superbly up until an untimely double fault saw Tsitsipas pinch the second set but the Spaniard, who has never won this title, responded well to reach the knockout stages for the sixth time overall and the first time since 2015.
During his on-court interview, Nadal said: "I think I played quite well for such a long time. A bad game in 5-4 of the second affected it a little bit. I was winning my serve quite comfortable until that moment.
"After that, everything changed a little bit. I think I started to serve a little bit worse but in general terms it has been a very positive match for me.
"To be in the semi-finals here in the last tournament of the year is an important thing. I'm happy for that and I'm looking forward to that semi-final against Daniil."
Tsitsipas's record against Nadal now stands at 1-6, with his only victory coming, somewhat unexpectedly, on clay in Madrid last spring.
This was the second year in a row that Nadal and Tsitsipas faced off in the final group match, with the world number two winning on that occasion but missing out on the last four to the Greek and Alexander Zverev.
Tsitsipas was unhappy with his performance in the third set, saying: "I fought very hard in the second set and played with the right intentions which gave me lots of opportunities.
"I'm quite disappointed with the third one. It didn't go as planned. I was rushing, I don't even know what I was trying to do, I was trying to be way, way too much aggressive. I should have handled it a little bit more clever and patiently."
Earlier, Andrey Rublev claimed his first victory at the tournament in his dead-rubber clash with Thiem, winning 6-2 7-5.
Thiem admitted he was a step short, saying: "Obviously I wanted to win the match 100 per cent but the first two matches were pretty tough, pretty long.
"So, of course, with the fact that I was already qualified in the back of my mind, it was maybe difficult today to keep that intensity alive."
The third seed will feature the winner of Friday's clash between Novak Djokovic and Alexander Zverev in the last four.