Djokovic beats Federer to win fourth straight World Tour Finals

Djokovic's 6-3 6-4 victory over Roger Federer made him the first man ever to win the season-ending tournament four times in a row and left one of his biggest rivals where they have been all year, trailing helplessly in his wake.

The result also means Andy Murray is guaranteed to finish the year ahead of Federer at world number two for the first time.

Had Djokovic won the French Open, there would surely be no argument about it being the best season in tennis history.

The only tournament in which he did not reach the final was his first of the season, with Djokovic the first man ever to reach 15 consecutive finals in a season, and his haul included three grand slams and six Masters series trophies.

At 28, Djokovic already has 10 grand slam titles, seven short of Federer's record, and, worryingly for the rest, there is no sign that his appetite is sated.

The Serbian said: "It's been a great year with many highlights. If I can, I would pick obviously grand slam wins, especially the Wimbledon and US Open. I think this tournament, as well.

"Again, I've played maybe the best tennis of the season in China. I played great on clay, as well. Overall it's been as close to perfection as it can get.

"I'm just blessed and overwhelmed with the emotion and the thrill to be achieving such a great season. It inspires me even more to keep on going and hopefully playing on this level in the future.

"I'm convinced with this dedication to the sport, I can achieve more. How much, I don't know. I don't have a sense of urgency. I don't chase anything. I just try to be in the moment and see where it takes me."

This was the eighth meeting of the year between Djokovic and Federer, who played off for both the Wimbledon and US Open titles, both won by Djokovic.

But the world number one had been far from his best when they met in the group stages at the O2 Arena on Tuesday, suffering his first loss in 24 matches and first indoors since 2012.

However, any question marks about his form were put to bed by a ruthless display against Rafael Nadal in the semi-finals.

Federer went into the final unbeaten and chasing a record seventh title at the event. At least he was able to take to the court, which was not the case last year when back problems forced him to withdraw ahead of the final, handing Djokovic the title.

The Serbian made his breakthrough in the third game of the final and Federer just could not find the consistency he needed to counter his opponent's relentless excellence.

When Federer won five points in a row to recover from 0-40 at 3-4 in the second set, earning roars of appreciation from his faithful devotees, it seemed a key moment.

But it was as if it never happened as Djokovic held serve to love in the next game and then piled the pressure on again when Federer served to stay in the match.

This time he could not pull off a miracle, double-faulting on Djokovic's second match point. It was the world number one's fifth title overall at the tournament - one short of Federer's record - and was the perfect 48th birthday present for his coach Boris Becker.

Remarkably, the result means after 90 matches against Federer and Nadal, Djokovic is tied with both.

Federer had a couple of regrets, saying: "It would have been nice to serve a little bit better early on in the match, play better overall on his second serve, because he does allow you to play on his second serve.

"Maybe at times I went for too much. The moments where I should have gone safe, I didn't, and vice versa. If I played the match again, that is what I would try to do different.

"Other than that, I thought it was a good match. It was close. The first six games were tough, to be down 4-2. I had my chances to at least be even. But I thought he played well."