Tennis: Shanghai walkover boost for Del Potro

SHANGHAI - Argentina's Juan Martin del Potro reached the Shanghai Masters quarter-finals on Thursday without even picking up a racquet after German veteran Tommy Haas withdrew from their third round match with a back injury.

Sixth seed Del Potro, 25, faced a potentially tricky tie against the former world number two, who reached the quarter-finals in Shanghai last year, as he bids to reach next month's World Tour Finals in London.

Former US Open champion Del Potro, who won the Japan Open on Sunday, was waiting to take to the court but returned to the locker room when told the 35-year-old 11th seed had withdrawn.

Del Potro next faces either Spain's Nicolas Almagro or fourth seed Tomas Berdych of the Czech Republic as he bids to reach the season-ending showpiece.

The top three seeds in Shanghai, Novak Djokovic, Rafael Nadal and David Ferrer, have already qualified for the event, which features the season's top eight players. Del Potro is fifth in the Race to London, just behind Ferrer.