LONDON - Roger Federer lit up the O2 Arena with a dazzling 6-4 6-3 defeat of Novak Djokovic to hand the Serb an early ATP Finals exit and wreck his bid to end the year ranked number one.
In the 49th meeting between the 2 great rivals, Federer snapped a 5-match losing run against Djokovic and gained some consolation for his heartbreaking Wimbledon final defeat.
After both men had been beaten by Dominic Thiem earlier in the group, their eagerly-anticipated duel was a straight shoot-out to join the Austrian in the semi-finals.
Cheered on by the majority of the 17,000 fans in the arena, Federer produced an astonishing display of power, grace and precision and Djokovic simply had no answer.
Djokovic's first defeat by Federer for 4 years means Rafael Nadal will end the year as world number one for the fifth time even if the Spaniard fails to reach the semi-finals.
Nadal takes on Stefanos Tsitsipas in the other group on Friday.
Federer had played down talk of revenge when asked about his impending clash with Djokovic, but his victory celebration showed exactly what it meant.
"It was a great performance tonight from me," Federer, who at 38 continues to defy the passing years, said on court.
Asked what he did differently to the Wimbledon final when he failed to convert 2 championship points against Djokovic, the 20-time Grand Slam champion said: "I won the match point!"
Djokovic said it had been a "bad match" from his side but admitted Federer had done everything right.
"He was the better player in all aspects," the 32-year-old said. "I have the utmost admiration for him. What he's still showing on the court is phenomenal."
England's soccer team was in action across the city at Wembley on Thursday, but when Federer and Djokovic are on the same tennis court it is always the hottest ticket in town.
Djokovic had reached the final on his last 6 appearances at the ATP's most exclusive event while 6-time champion Federer had only once failed to reach the semi-finals in his 16 previous appearances.
Something had to give. From the moment Djokovic double-faulted twice in the third game to invite an early break for Federer, his hopes of extending his proud record looked forlorn.
Federer was seeing the ball like a melon, timing his groundstrokes to perfection while his serve was unplayable.
He dropped only 3 points on serve in the opening set and Djokovic's only chance was that Federer would cool off.
Djokovic dug deep to fend off break points in the opening game of the second set, then had his one and only break point in the fourth game but Federer whipped a huge forehand into the corner before pouncing on a volley.
Federer was relentless and surged 0-40 ahead in the next game. Djokovic saved one break point with a backhand pass but hit a forehand long on the next.
The end came quickly. Serving to stay in the match, Djokovic was broken to love as Federer sent a dipping backhand to his feet.
Earlier in the day Matteo Berrettini became the first Italian to win a match at the ATP's year-ender, beating Thiem 7-6(3) 6-3. Despite the loss, Thiem won the group by virtue of his victory over Federer on Sunday.