Roger Federer still confident

  Six-time champion Federer has only once failed to reach the last four in 11 previous appearances at the end-of-season event and never at London's O2 Arena.

It says everything about the year Federer has had that Del Potro will go into the match as the favourite, but the odds are less weighted in the Argentinian's favour than they would have been a couple of weeks ago.

Although Federer is still not completely sure about his game, his confidence has been boosted by a run to the final in his home town of Basle and then a semi-final appearance at the Paris Masters in the last fortnight.

He played Del Potro in both events, losing in Basle but then winning their clash in Paris, the first time he had beaten the world number five in four matches.

Federer said: "I think the win in Paris was big for me, because he did beat me three times indoors straight, the Basel finals twice, and also here last year Nadal edged out Berdych

"Then I was already qualified, so those matches are hard to manage. But I tried, I fought, and he did better.