I'm at the pinnacle in my career: Djokovic

‘I physically feel very fit. I'm very motivated to keep on playing on a very high level’

Novak Djokovic laid down the challenge to his rivals on Sunday after completing another year as World No 1.

Djokovic wins ATP year-ender after Federer pulls out

"Right now, I'm at the pinnacle in my career," the 27-year-old Serb declared after claiming a third consecutive ATP World Tour Finals title by default when Roger Federer withdrew before their showpiece final with a back injury.

"I physically feel very fit. I'm very motivated to keep on playing on a very high level. I'm going to try to use these years in front of me to fight for the No 1 of the world and fight for the biggest titles."

Djokovic ends the season as No 1 for the third time in four years having won a seventh Grand Slam at Wimbledon and Masters 1000 titles in Miami, Indian Wells, Rome, Paris and this week's year-ender in London.

While arch-rival Rafael Nadal is still recovering from a wrist injury followed by appendicitis, Andy Murray is struggling to return to his best form after back surgery a year ago and 33-year-old Federer cannot hold back time forever, new dad Djokovic appears to be reaching his prime.

In London, he dropped only nine games in his three group matches before seeing off Japan's Kei Nishikori in the semis and he will start 2015 having clearly set the benchmark for men's tennis.

‘It's a very awkward situation to talk about it’

Djokovic said he was disappointed his year ended with a hollow victory -- even if it meant he was the first to win the year-ender three times in succession since Ivan Lendl.

"This is probably the first time in history that this happens," said Djokovic, who found out shortly before the final that Federer was withdrawing.

"It's a very awkward situation to talk about it, to be honest. You never like to win, especially these big matches against big rivals, with a retirement."

‘This is one of the biggest matches of the year for him, as well as for me’

Djokovic rejected any suggestion that Federer had pulled out to save himself for next week's Davis Cup final.

"The stats are saying clearly that he is one of those players that would compete and always fight if he can," Djokovic said. "He has had, what, three retirements in his entire career?

"I don't think he was calculating and trying to save his body for the Davis Cup final. I'm sure that wasn't the case. This is probably one of the biggest matches of the year for him, as well as for me."