London - Home hero Andy Murray faces Argentina's US Open champion Juan Del Potro Sunday with Roger Federer to follow as Group A matches start the ATP World Tour Finals.

Roger Federer, who could possibly lose his number one ranking to Rafael Nadal under certain scenarios, will face Spain's Fernando Verdasco on the opening day at the O2 Arena.

The Swiss lost his US Open crown to Del Potro in September, before the newest Grand Slam winner hit a patch of bad form in the autumn.

Spain's Nadal begins starts in Group B on Monday against Robin Soderling, a re-run of the Roland Garros fourth round which he lost. Soderling replaced injured Andy Roddick in the eight-man field.

Novak Djokovic, winner of the last pair of ATP titles this season, takes on Russian Nikolay Davydenko. (dpa)