Roger Federer produced a serving masterclass as he avenged his Wimbledon defeat by Novak Djokovic and qualified for the last four of the ATP Finals on Thursday with a 6-4, 6-3 victory.
The Swiss broke once in the first set and twice in the second to beat his rival for the first time since 2015.
Roared on by a raucous packed house at London’s O2 Arena, the Swiss six-time champion broke early and dropped just seven points on his serve in the first set.
Defeat spells the end of Djokovic’s bid to overtake Rafael Nadal and finish as year-end number one.
Djokovic looked nervy at the start of the winner-takes-all contest, double-faulting twice in the third game, in which he was broken to love.
As cries of “Let’s go Roger, let’s go” rang around the cavernous stadium, Federer was dead-eyed on his serve, hitting eight aces, including a second-serve ace, in the first set.
Federer’s service level dipped in the second set and Djokovic earned his first break point of the match in the fourth game, which the Swiss saved.
He broke Djokovic again in the fifth game to take an iron grip on the match and broke again to seal the win.
The Swiss third seed joins Austria’s Dominic Thiem, who had already qualified from Group Bjorn Borg, in the semi-finals.
It was the 49th time Federer and Djokovic had met.
Djokovic, who now holds a 26-23 advantage, had won their past five meetings, including their epic five-set battle in the final at Wimbledon in July, during which he saved two championship points.
In Thursday’s early match in Group Bjorn Borg, which was a dead rubber, eighth seed Berrettini beat Thiem 7-6 (7/3), 6-3.
In doing so, the 23-year-old became the first Italian to win a match at the season-ending championships.
Berrettini arrived in London at a career-high number eight in the ATP rankings after starting the season outside of the top 50.
Fifth-seed Thiem did not hit the heights he reached during his three-set win against Djokovic, notching just 12 winners compared with 50 against the Serbian.
Stefanos Tsitsipas has already qualified for the semi-finals from Group Andre Agassi, leaving Nadal, defending champion Alexander Zverev and Daniil Medvedev to scrap it out for the other spot on Friday.