Fourth seed Andy Roddick has been forced out of the Shanghai Masters with an injury to his left knee.

Wimbledon finalist Roddick was 4-3 up on Switzerland's Stanislas Wawrinka in the first set when he was unable to continue.

Elsewhere in the second round, sixth seed Nikolay Davydenko defeated fellow Russian Igor Kunitsyn 6-4 6-2 and 10th seed Fernando Gonzalez saw off Brazilian qualifier Thomaz Bellucci 6-3 6-3.

Radek Stepanek also booked his place in the third round with a 7-5 6-4 victory over Germany's Andreas Beck.

In today's first round matches, Lleyton Hewitt made light of a significant height disadvantage to beat American John Isner 6-2 6-4, even lobbing the 6ft 9in American on more than one occasion.

There were also straight sets wins for ninth seed Robin Soderling over Victor Hanescu, 11th seed Gael Monfils over fellow Frenchman Paul-Henri Mathieu and Tommy Haas over compatriot Benjamin Becker.

However, 12th seed Marin Cilic lost in three sets to Tomas Berdych of the Czech Republic.