Revenge was sweet for Roger Federer as he won his shoot-out with Novak Djokovic to reach the last four at the ATP Finals in London.
The 38-year-old avenged his agonising Wimbledon final defeat by Djokovic in July, winning 6-4 6-3 on Thursday to deny the Serbian the world number one spot in the process.
The illustrious pair, with 11 titles between them, were both expected to progress from the group stage but Dominic Thiem's impressive form meant only one of them could join him.
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It was Federer who maintained his proud record of having never failed to reach the semi-finals at The 02, and he can now bid for a record seventh title over the weekend.
Four years since his last win over Djokovic, and four months since he blew those two championship points at Wimbledon, an elated Federer said: "It was a great atmosphere, a great opponent, here at the 02, incredibly special, I enjoyed it from the beginning.
"What did I do differently from Wimbledon? I won the match point I guess.
"You move on, try harder next time round and hope the luck goes for you. I couldn't be happier right now."
Federer can now put his feet up ahead of a semi-final showdown with Stefanos Tsitsipas, Alexander Zverev, Daniil Medvedev or Rafael Nadal, who is now guaranteed to end the year at the top of the rankings.
"You always play better as a tournament goes along," added Federer.
"Dominic has been supreme in our group and put us in this situation, there was a lot riding on the match. I had a clear game plan and it worked to perfection. It was a great performance from me tonight.
"Am I looking forward to the weekend? A lot. I'm happy to stick around. I didn't make any plans yet!"
Djokovic, who failed to reach the semi-finals for the first time since 2011, said: "There was not much that I did right this match, to be honest.
"He served great, moved well, returned my serve very well. From his end, I think he did everything right.
"I mean, realistically he was better player in all aspects and absolutely deserved to win.
In the afternoon's dead rubber, Thiem was beaten 7-6 (7-3) 6-3 by Matteo Berrettini, who ended his stay in the English capital on a high by becoming the first Italian to win a match at the Finals.