Dominic Thiem produced a burst of big-hitting to beat Novak Djokovic in a final-set tie-break and reach the final of the ATP Finals.
The Austrian looked set to miss out on a golden opportunity as he trailed 4-0 in the breaker, at the end of a match he'd dominated only to pass up a series of match points in the second set.
But from there he found a final surge, taking the next five points and finally completing the job to become the first man since 2016 to beat Djokovic and Rafael Nadal in the same tournament.
Thiem will now face Daniil Medvedev in Sunday's final, after the Russian conjured an inspired fightback to beat Rafael Nadal in three sets on a fabulous day of tennis.
Speaking on court, Thiem said: “It was for sure a mental battle. I got so tight in the second-set tie-break. To play these big legends is always something special, playing for a finals here is also something very special.
“I thought that after my first big title in New York maybe I’m going to be a bit more calm, but it was a mistake I guess. It was so much on the edge this match. I’m just incredibly happy to be through and will just try to get ready for the final.”
Djokovic won four straight titles in London from 2012 to 2015 but his efforts to equal Roger Federer’s record of six victories have come to nothing since.
Having not lost a completed match until the French Open final last month, meanwhile, his season has ended with a run of four losses in eight matches.
The 33-year-old was well below his best in a round-robin loss to Medvedev and, although he was much improved in his must-win contest with Alexander Zverev on Friday, there were still uncharacteristic errors.
Here, Djokovic was solid if not spectacular for the first 10 games while Thiem showed his frustration at a lack of precision.
The 11th game gave the third seed his breakthrough, though, as Djokovic unwisely kept coming forward and paid the price, dumping a volley into the net on the first break point of the match.
The world number one was criticised in his French Open final hammering by Nadal for overplaying the drop shot, and here he seemed to have replaced that with the drop volley.
Thiem confidently served out the first set and Djokovic looked hurried and harassed as he faced another break point in the fifth game of the second set, but this time his opponent netted a forehand.
This was the latest in a series of close matches played out between these two. Last year at The O2, Thiem won an epic group match, while Djokovic edged a five-set Australian Open final in January.
Djokovic had his first break point of the match at 4-3 but narrowly missed a return, while a couple of errors from Thiem presented his opponent with two set points at 6-5 but again the greatest returner the game has seen was unable to get the serve back.
Djokovic seemed to be having trouble freeing himself up but he was certainly not the only player feeling the tension in an extraordinary tie-break.
Thiem served a double fault on the second match point and missed a forehand on the third, while a netted backhand on Djokovic’s second set point was the decisive moment.
It was nip and tuck all through the decider as well, but the momentum seemed to be gradually moving Djokovic’s way.
He let out a huge roar of frustration at a missed return at 5-4, 30-30, but that was nothing to the disappointment he must have experienced as Thiem wrestled the tie-break away from him.
Having played four poor points at the beginning, Thiem went for broke and it paid off spectacularly, leaving Djokovic helpless and heading home.
Med to measure
Medvedev then staged an impressive comeback to defeat Nadal for the first time and set up a Nitto ATP Finals decider against Thiem.
A glance at the grand slam winners’ list will show that the old guard are still rightful leaders of the pack but the snapping at their heels has more bite now, particularly from Thiem and Medvedev.
Having seen Thiem somehow recover from 0-4 in a deciding tie-break to beat Djokovic in the first semi-final, Medvedev clawed his way back from a set and a break down to beat Nadal 3-6 7-6 (4) 6-3.
That maintained his record of not having lost a match this week and, coupled with his victory at the Paris Masters earlier this month, he is now on a nine-match winning streak.
Nadal, whose search for the biggest title he has yet to claim goes on, had won all his three previous clashes with Medvedev but the last two had been exceptionally close.
Medvedev fought back from two sets down in his first grand slam final at the US Open last year only to lose in five, while in London last year he led 5-1 in the deciding set of a round-robin match before, in his own words, choking.
So impressive had the Russian been this week, particularly in a convincing win over Djokovic, that most pundits made him the favourite and Nadal was forced to save three break points in the third game.
But the Spaniard has been very upbeat about his own level, even after losing to Thiem, and, when Medvedev failed to land a first serve at 4-3, Nadal pounced.
The world number two had won 71 straight matches in which he had taken the opening set so the size of Medvedev’s task was clear.
He received a helping hand at the start of the second set, though, when Nadal double-faulted on break point in the second game, and the second seed had to save another break point to avoid going 5-1 behind.
That looked set to be the crucial moment as Nadal played a brilliant returning game to get back on serve and, the doubts now sown in Medvedev’s mind, made it four games in a row to move to the brink of victory.
But the Russian, who did not win a match at The O2 on his debut last year, was not finished and played a perfect returning game to break Nadal to love when he served for the match.
Medvedev opened up a 6-3 lead in the tie-break, partly thanks to an outrageous shank that looped over Nadal, and this time the Spaniard could not find a way back.
Nadal had quickly regained the initiative after losing the second set against Stefanos Tsitsipas on Thursday but here he had to fight off another break point at the start of the decider.
Unusually it was a lack of ruthlessness from the Spaniard that cost him as he failed to take several chances to hold serve at 3-3. Medvedev seized his opportunity and did not let go.