Novak Djokovic set his sights on the Australian Open after a painful defeat in the ATP Finals at the hands of Alexander Zverev took some of the gloss off an incredible season.

The Serbian world number one looked unbeatable heading into Sunday’s final, winning all four of his matches in London in straight sets and not dropping serve once.

But his 21-year-old opponent showed no fear at a packed O2 Arena, trading heavy blows with his illustrious opponent from the back of the court and outlasting him in long rallies to win 6-4, 6-3.

A sanguine Djokovic was eager to put the defeat into context after a memorable second half of the season, during which he has clambered back to the top of the men’s game from the lowly ranking of 22 he found himself in as recently as June.

“Obviously no one likes to lose a tennis match,” he said. “You try your best. But at the same time, as I said on the court, you put things in a larger perspective, see things a bit differently.

“When you get out of this feeling of a little bit disappointment that you lost, I mean, all the positive things that I have to reflect on and also take from this season, especially the last six months.”

The 31-year-old started his year with a miserable early exit at the Australian Open, followed by elbow surgery and a string of disappointing results on his return to the court.

But since Wimbledon started he has suffered just three defeats — including Sunday’s against Zverev — winning a fourth title at the All England club and following up by securing a third US Open crown to leave him on 14 Grand Slams — three behind Rafael Nadal and six behind Federer.

“Overall it was a phenomenal season that I have to be definitely very proud of,” Djokovic said.

What is frightening for Djokovic’s rivals is that — Sunday’s surprise defeat aside — he appears to be getting better.

– Serving power –

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Widely regarded as one of the greatest returners in the history of the game, it is his serving numbers that have been so striking during his run to the final in London.

Federer remains a threat and Nadal and Andy Murray are on the road back from injury while Zverev will start next season full of confidence despite his poor record at Grand Slams.

But Djokovic will be the man to beat when the first major of next year comes round in Melbourne in January — it is a venue where he has won six times.

“Having a Grand Slam so early in the season makes us train probably very hard and be kind of aware that we have to be at our best in the first week of the year,” he said.

“The first Slam is there in January. I’ve had most success in my life, in my career, in Australia out of all four Slams. Hopefully I can keep that going.”