Alexander Zverev beat Novak Djokovic in the semi-final of the ATP Tour finals 7-6(7-4) 4-6 6-3.
Djokovic was looking for a second consecutive tournament win after winning the Paris Masters, and he was up against Zverev.
The pair were playing for a chance to take on 2020 champion Daniil Medvedev, who had beaten Djokovic in the US Open final in September.
Australian Open
Order of play, Day 10: Medvedev in top-10 battle, Cornet and Kanepi chase first semis
Tokyo Olympic champion Zverev went toe-to-toe with the Serbian world number one and the first set almost inevitably went to a tie-break as the pair struggled to gain an edge.
A 7-4 scoreline gave the Russian the first set and left Djokovic on the back foot in the semi-final.
With his back against the wall in the second set, Djokovic knew he had to win and broke his opponent late on, and moved into a 5-4 lead to stay in contention and force a third set.
Djokovic sealed the second, and Zverev responded to break his rival to go 3-1 up in the third with a real chance of reaching the final, and he held his nerve to move 5-2 up, just a game away, before securing an ultimately comfortable win. For once, Djokovic could not mount a comeback.
Australian Open
'It should be equal for everyone' - Shapovalov hits out after testy Nadal clash
Australian Open
The must-watch interview and moody Medvedev – AO Diary