LONDON: Roger Federer produced a near-flawless performance as he avenged his Wimbledon defeat by Novak Djokovic and qualified for the last four of the ATP Finals with a 6-4, 6-3 victory on Thursday (Nov 14).
The Swiss started the tournament with a chastening straight-sets defeat to Dominic Thiem but found his best form when it mattered.
Defeat for the second seed spells the end of his bid to overtake Rafael Nadal and finish as year-end number one.
Roared on by a raucous packed house at London's O2 Arena, six-time champion Federer looked in the groove from the start, cranking up the pressure on Djokovic's serve and dropping just three points on his own serve in the whole set.
The Serbian upped his game at the start of the second set but Federer saved the one break point he faced and broke twice to canter to victory.
The third seed, making his 17th appearance at the ATP Finals, is into his 16th semi-final at the year-end event.
Djokovic needed to win the title to have a chance at knocking Nadal off the top spot, but now the Spaniard is guaranteed to finish the year as the top-ranked player for the fifth time, tying him with Federer, Djokovic and American Jimmy Connors.
"Great atmosphere, great opponent," said Federer. "It was definitely incredibly special. I enjoyed it from the beginning.
"I played incredible and I knew I had to because that's what Novak does. It was definitely magical. You guys made it super special, I can't thank you enough."
Speaking about what was different from Wimbledon, he said: "I won match point I guess. It was so close at Wimbledon. It was a privilege to play that match, so many ups and downs. I couldn't be more happy right now."
Federer finishes second in Group Bjorn Borg, behind Dominic Thiem, who beat both Federer and Djokovic earlier this week. The Swiss will face the Group Andre Agassi winner on Saturday.
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 repeated the trick to take the second set 6-3.
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.
Djokovic admitted Federer deserved to win, saying he "did everything right" and admitting he himself had played badly.
But he said he was happy with his season overall, adding: "If I have to draw the line, I think it was still a very good season, winning two Slams and five titles."
In Thursday's early match in Group Bjorn Borg, which was a dead rubber, eighth seed Matteo 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.
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.