Djokovic was lifting the trophy for the fifth time in his career
Novak Djokovic capped a remarkable season with victory over Roger Federer to claim a record fourth straight ATP World Tour Finals title.
The world number one from Serbia won 6-3 6-4 in 80 minutes at London's O2 Arena.
Djokovic also made amends for defeat by six-time champion Federer in the group stage on Tuesday.
"I am enjoying every moment on the court, I cherish every moment after dreaming of it as a kid," he said.
He ends the year with 11 titles including three Grand Slams, taking his total to 10 majors.
The 28-year-old has now won the season finale five times and surpasses Ivan Lendl's 1987 achievement, when he won his third straight Tour Finals title in New York.
Federer said: "It is never fun on the not winning side, it is better than not playing at all like last year. This week was great, there were some crazy points tonight, but like plenty of times this year Novak deserved it."
The defeat by Federer on Tuesday had been his first indoors since 2012, but Djokovic responded in simply irresistible style as he despatched first Rafael Nadal and then, in the final, Federer.
It ended with a double fault as even the 17-time Grand Slam champion wilted under the pressure of such relentless accuracy from his opponent.
Aside from the trophy, another 1,300 ranking points and the cheque for £1.4m, Djokovic also draws level with Federer at 22-22 in career meetings.
The pair have shared 11 of the last 13 season-ending titles between them, but it is the Serb who now dominates.
Andy Murray finishes 2015 as world number two
Djokovic's victory ended Federer's chance of overtaking Andy Murray in the rankings, meaning the Briton will end the year as world number two for the first time
Federer, 34, had been quick to play down the significance of his group-stage win and Djokovic did indeed prove a very different opponent in the final, just as he had at Wimbledon and the US Open.
The Swiss needed to be clinical but forehand and backhand errors saw him miss both break points in the first set, and Djokovic capitalised.
A brilliant cross-court backhand set up the top seed to break in game three, and Federer had racked up 16 errors by the time he was broken for a second time to drop the set.
The better part of 17,800 spectators urged on the Swiss as he kept pace in the second set, levelling at 3-3 with a shout of "Come on!", but Djokovic remained unmoved.
Winning a stunning 84% of points on his second serve as Federer failed to make a sustained assault, and after failing to convert from 0-40 in game eight, Djokovic clinched victory two games later.
Djokovic shows off the trophy to photographers at the 02 Arena
Federer looks on following his straight-sets defeat by Djokovic