Writing off Roger Federer as a threat for the game's biggest titles has become something of a sport in itself in 2013 but the Swiss believes he has a chance to end it on an unlikely high by winning the Barclays ATP World Tour Finals, which begin today at London's O2.

While Rafael Nadal and Novak Djokovic have the small matter of the end-of-the-year world No.1 ranking to play for, as well as the title, the 32-year-old Federer is desperate to remind his peers that he is not done just yet, despite dropping to No.6.

The defending champion, Djokovic, unbeaten since the US Open, is the favourite ahead of world No.1 Nadal, for whom this time of the season has always proved the most troublesome. Even Juan Martin del Potro is above Federer in the betting, but the six-times champion has been boosted by good performances in Basle and Paris and feels he can do some damage.

"I'm happy with my game and the confidence is back again," Federer said yesterday, having hot-footed it from Paris, where he reached the semi-finals of the BNP Paribas Masters. "That can carry you a long way."

With Andy Murray missing out as he continues to recover after back surgery, Federer will not have any competition when it comes to crowd favouritism. Even when he played Murray here last year, the crowd was 60-40 for Federer and there were even a number of boos for the Scot, as Swiss fans made their voices clear.

This will be the 12th consecutive appearance in the season-ending event for Federer - equalling Ivan Lendl's record - and the Swiss fans traditionally buy their tickets in bulk, months in advance, safe in the knowledge that he will be there.

This time, it took until the last week to secure his place, evidence of just how tough a year he has had to endure, largely, he said recently, because of back trouble.

"I know that the year has been a bit more difficult," he said. "Most of the time I was just focusing on myself to get things right in my life with my back and so forth. Now finally that I did I feel like it's coming together at the right time for me.

"But it has a different feel because it just hasn't been as consistent, as good and as solid as it has been in previous years, so I'm maybe still a bit more unsure about how high my level of play has been, even though it has been pretty good the last couple of weeks."

The task facing Federer, though, is a fierce one. His win over Del Potro last week in Paris was his first victory over a top-five player this year and he has been drawn in the tougher group alongside the Argentine, Djokovic and Richard Gasquet of France.

Moreover, his first round-robin match will be against Djokovic tomorrow. Either man can lose and still qualify and Federer knows more than most that this week's event is a marathon, not a sprint.

"It is a test of endurance and a mental fight," he said. "For some, it's not over yet. Some have come off two tournaments played like me, some off three. Some have Davis Cup after this, so it's a true test."

Switzerland have two players in the event for the first time after the qualification of Stanislas Wawrinka, who joins Nadal, David Ferrer and Tomas Berdych in the other round-robin group. Wawrinka opens the tournament today against Berdych.

Nadal, who has never won the event, plays Ferrer in his first match tomorrow, a chance for revenge over his fellow Spaniard for his defeat in the semi-finals in Paris last week.