Roger Federer: Win over Novak Djokovic made it a special night at World Tour Finals
Roger Federer described it as a "special night" after beating world number one Novak Djokovic 7-6 6-2 in the World Tour Finals at the O2 Arena in London.
It was a first defeat indoors for Djokovic since 2012, although he can still make it through the group stage and into the semi-finals.
Djokovic must beat Tomas Berdych, who himself still has a chance of qualifying, to guarantee his spot in the last four.
"It's always a thrill to come out here, even more so against a great player like Novak," said Federer after clinching victory on his second match point.
"It's a special night for tennis, and a cool atmosphere," the Swiss said. Victory guarantees Federer a place in the last four.
Kei Nishikori boosted his hopes of reaching the semi-finals with a battling victory over Tomas Berdych.
After four straight-sets singles matches this was a contest the tournament needed and it was Nishikori who came through 7-5 3-6 6-3 after two hours and 23 minutes.
Jamie Murray and John Peers have work to do to reach the semi-finals of the ATP World Tour Finals after losing their second match at the O2 Arena.
Murray and Peers marked their debut on Sunday by beating Fabio Fognini and Simone Bolelli, but Rohan Bopanna and Florin Mergea proved a tougher nut to crack.
The Indian/Romanian duo followed up their victory over the Bryan brothers by winning 6-3 7-6 (7/5) to book their spot in the last four.
Murray and Peers now almost certainly have to beat the top-ranked Bryans in their final group match on Thursday if they are to make the semi-finals.
They made a bad start when Peers double-faulted to give up a break in the second game, and four missed chances in the following game were the only ones they had to claw back the deficit in the opening set.
The writing looked on the wall when Murray, who was named in Great Britain's team for the Davis Cup final on Tuesday, was broken in the seventh game of the second set having hit Peers in the back of the neck with a shot.
But two loose shots from Mergea handed the break straight back, and Murray and Peers then fought off another break point thanks to a remarkable shot from the Scot.
He turned away in self defence as the ball flew at him from close range but it hit the edge of his frame, looped up onto the baseline and Bopanna missed his smash.
The stroke of luck did not prove a turning point, though, as Bopanna and Mergea won the second-set tie-break 7-5.
Meanwhile, Kyle Edmund and James Ward will fight it out for a place in Great Britain's Davis Cup final team after a decision on Aljaz Bedene's appeal was deferred until March.
The British number two is currently ineligible to play for his adopted country because of a change in the rules in January barring players from competing for two different nations.
Bedene, who has lived in Britain since 2008, had previously played three dead rubbers for his native Slovenia.
He travelled to Prague with a lawyer from the Lawn Tennis Association to present his case to the International Tennis Federation Board, and had he been successful he could have come into contention for the final.
But instead the 26-year-old must wait another four months to find out the verdict, a full year after he was granted a British passport.