Roger Federer opened the ATP World Tour Finals with a hard-earned victory over Jo-Wilfried Tsonga at London's O2 Arena.
Bidding to defend the title he won 12 months ago and secure a record sixth season-ending crown, Federer came through 6-2 2-6 6-4 in one hour and 28 minutes.
The 16-time Grand Slam champion looked on course for a routine triumph when he dominated the first set, breaking twice and dropping only three points on serve.
Tsonga responded brilliantly in the second set with two breaks of his own to level, and he continued to take the fight to Federer in the decider.
But the Swiss legend showed all his class and experience to strike late on and make an early move to the top of round-robin Group B.
After the match Federer said: "Jo-Wilfried served well in the second set and it was hard to control the rallies at the baseline. But I think this is the best I've played all year. It helped that I had some good time off before playing great at Basel and Paris."
Tsonga added: "I think he was a bit surprised because I played so bad in the first set, then I played correctly in the second, but it's always difficult because he's really quick.
"Sometimes you think you will get the point but Roger is still there. That's why it's tough to play against him."
The evening match sees world number two Rafael Nadal face Mardy Fish at 2000 GMT, with Andy Murray and Novak Djokovic both in Group A action on Monday.
Federer arrived in London as the man to beat, with 17 wins from his past 18 matches and victory - over Tsonga - at the last Masters 1000 event of the year in Paris.
He had won six of his nine previous encounters with the Frenchman, although they had never met indoors before and Tsonga stunned Federer in this year's Wimbledon quarter-finals.
With two of the sport's most eye-catching players first up and music, bright lights and dry ice used to build the atmosphere, there was a palpable sense of excitement around the 17,500-capacity venue.
The noise was deafening when they emerged on court with both men backed by large sections of the crowd but Federer certainly the favourite.
His mother Lynette, wife Mirka and French footballer Thierry Henry - not supporting compatriot Tsonga - looked on in awe as the world number four put on a first-set masterclass.
Federer's serve looked smooth from the outset as he held to love in his opening service game and, with his opponent struggling for rhythm, he went all out attack in game three.
Two forehands were flicked wide by Tsonga to hand over an easy break, and Federer struck again in the eighth game when the world number six produced three more errors and a double-fault.
At this stage, Tsonga had only managed to win three points on the Federer serve.
But the second set was a different story as the 6ft 2in right-hander began hitting with much greater accuracy, depth and consistency.
Federer failed to control a forehand to go down a break after three games, and it was the same shot that uncharacteristically let him down to fall 5-2 behind.
Tsonga served out confidently and bounced back to his chair with a spring in his step as his support team in the stands rose to their feet.
His service statistics improved dramatically in a disciplined third set, yet Federer stayed calm and the worst position he faced on his own delivery was deuce at 1-1.
There was a feeling around the arena that Federer was saving himself for one final push - and so it proved when he broke to 15 in the 10th game to seal the win.
In the opening doubles match of the Finals third seeds Max Mirnyi and Daniel Nestor beat fifth seeds Rohan Bopanna and Aisam-ul-Haq Qureshi 7-6 (7-2) 4-6 11-9.