Roger Federer became the first player to win the ATP World Tour Finals six times but had to weather a storming fightback by Jo-Wilfried Tsonga before retaining his title with a 6-3, 6-7, 6-3 victory at the O2 on Sunday.

The 30-year-old, playing in the title match of the tournament for the seventh time in 10 years and contesting his 100th Tour final, squandered a match point in the second set but eventually extinguished Tsonga's fire to claim the 70th title of a career that burns as bright as ever.

On yet another record-breaking day for the 16-times Grand Slam champion, Federer not only edged clear of five-timers Ivan Lendl and Pete Sampras in the tournament's roll of honour but he also gained the distinction of being the oldest player to win the season-ender since Ilie Nastase in 1975.

It took all his years of experience and a few moments of magic to withstand Tsonga's force, however, as the explosive Frenchman thrilled the 17,500-capacity crowd with a barrage of winners that threatened to turn the contest on its head.

After levelling the match Tsonga threw everything at Federer in the decider but he was stopped in his tracks when he dropped serve at 3-4 and this time there was no escape as the Swiss pounded away a volley to triumph in two hours 18 minutes.

"I couldn't be more happy and I couldn't be more exhausted because Jo sucked all the last energy out of me today," Federer said on court after sealing the $1.63 million jackpot for going through the tournament undefeated for the second year in a row.

"It feels very special," Federer, who climbs back above Andy Murray to No.3 in the rankings and will start next year eyeing Rafa Nadal and Novak Djokovic, said.

"I've been trying to sort of block it out for the entire tournament. So now it's finally sort of reality that I've been able to win six World Tour Finals. It's an amazing feeling. I know it's one of my greatest accomplishments.

"This definitely is an amazing finish again to the season. I've never finished so strong."

Bizarrely, it was the third successive Sunday that Federer and Tsonga faced each other across a net.

Tsonga, bidding to become the first Frenchman to win the season-ending championship since its inception in 1970, began in impressive fashion, though, and looked the more menacing player until Federer found a spark to break serve to love in the eighth game when Tsonga fluffed a backhand volley.

A forehand winner gave Federer a break midway through the second set and a routine victory beckoned until the match unexpectedly burst into life.

Serving for the title at 5-4, Federer came under attack by Tsonga who eked out his only break points of the match by going 0-40 ahead. Federer saved two but Tsonga pounced on a volley to level the set at 5-5 to the delight of a crowd that contained the Duchess of Cambridge and Real Madrid forward Cristiano Ronaldo.

Federer went 5-2 up in the tiebreak but even a man with 806 wins on the ATP Tour can get edgy and a passive match point at 6-5 was punished by a belting Tsonga winner.

Tsonga then got a set point himself and gobbled up a weak Federer second serve to take the match to a final set shootout.

Federer kept his nose in front in the deciding set despite some ferocious hitting from Tsonga and, just like he did in the first set, broke in a gripping eighth game when Tsonga sent a volley long under enormous pressure.

Serving for the match for the second time, Federer made sure there was no mistake, setting three match points with an ace and then swatting away a volley.

Tsonga can take heart from winning over another army of fans and can look forward to threatening the Big Four next year.

"Tonight I can look at myself in the mirror and say I fought enough," he said.