Roger Federer celebrates after beating Frenchman Jo-Wilfried Tsonga in the ATP World Tour Finals at the O2 Arena in London Sunday. (Reuters)

LONDON (AP) — Roger Federer wasn't about to let Jo-Wilfried Tsonga pull off another improbable comeback.

After a year that saw some uncharacteristic slip-ups from Federer in big matches, the Swiss former No. 1 shrugged off a second-set letdown to beat Tsonga 6-3, 6-7 (6), 6-3 and put his name on yet another page of the history books by winning a record sixth title at the ATP World Tour Finals.

“I know it's one of my greatest accomplishments,” Federer said about his latest record. “This definitely is an amazing finish again to the season. I've never finished so strong.”

Federer was by far the most impressive player this whole week at the season-ending event for the top eight players in the world, where his three group-stage victories included his most comprehensive win ever over Rafael Nadal, beating the Spaniard 6-3, 6-0 on Tuesday.

But he looked in danger of faltering against Tsonga when he failed to serve out the match at 5-4 in the second set and then wasted a match point in the tiebreaker.

But Tsonga, who became the first player to rally from a two-set deficit to beat Federer in a Grand Slam tournament in this year's Wimbledon quarterfinals, couldn't pull off another surprise this time.

Playing in his 100th career final, Federer broke for a 5-3 lead in the decider and served out the match to love, sealing his 70th career title with an easy volley.

“I think that was the difference to other matches this year, where I lost so closely,” Federer said. “This time around I was still able to find a way through. I think that was the difference at times during the year, which didn't maybe make this an absolutely phenomenal year.”

Federer finished the season without a Grand Slam title for the first time since 2002, after also wasting a two-set lead against Novak Djokovic in the US Open semifinals – where the top-ranked Serb saved two match points in the fifth set.