Federer ranks World Tour Finals victory among his best
Roger Federer said winning a record sixth season-ending crown was "one of his greatest accomplishments".
The 16-time Grand Slam champion beat Jo-Wilfried Tsonga to end his year with victory at the ATP World Tour Finals.
"It feels very special indeed," said Federer, 30. "I know it's one of my greatest accomplishments. It was the strongest finish to a season I've ever had in my career."
He lifted titles in Basel and Paris before winning all his ties in London.
He has not lost since the US Open in September and will take a 17-match unbeaten streak into 2012.
"Right now I'm happy the season is over," said Federer, who finished without a Grand Slam trophy for the first time since 2002.
"It has been long and it has been gruelling, but I'm happy I'm still strong and healthy. I'm really excited for next year - I'm upbeat about what's to come."
A set and a break to the good, Federer looked on course for a routine victory over sixth seed Tsonga.
But the powerful Frenchman broke back and saved a match point to snatch the second set on a tie-break.
However, Federer came through strongly in the decider to collect a 70th title in his 100th career final.
"The relief was amazing," stated the Swiss. "Jo played well. Could I have won it easier? I guess; I had it in my hands.
"I had to go through the third set but eventually I made it, which probably felt even better. The joy was great."
Federer did, however, suggest the season-ending championship final should be the best-of-five sets rather than its current best-of-three format.
"If it's a match like this it's fine as there's enough tennis for the people," he commented. "But if I would have served it [the second set] out, it would have been over in a hurry.
"I think I almost felt the spectators weren't quite ready for it to end quite yet. Although many would have been happy for me, they would have loved to see more tennis.
"I remember sitting in a room in Shanghai where the players were asked, 'Would you like the year-end final to be five sets or three. Everyone said best-of-three sets. I was the only guy that said five.
"I do care actually. I think it makes for a great year end. Sure, you can see why maybe it's healthier to play best-of-three but I believe the final could be a best-of-five set match."
Tsonga was bidding to become the first French player to win this event but despite his defeat, he showed signs of being able to challenge the 'big four' of Federer, Novak Djokovic, Rafael Nadal and Andy Murray in 2012.
"I fought all I could," said the 2008 Australian Open runner-up. "I'm happy because I had a good week. I can look myself in the mirror and say I gave everything, I fought enough.
"I need to improve again. I have to work hard and be quicker on the court. If I can move better next year I will have some better results."