Belgian Steve Darcis upset Czech fourth seed Radek Stepanek 7-6 (7-4) 7-6 (7-2) on Thursday to reach the quarter-finals of the $US531,000 ($A498,217.30) ATP San Jose Open.

Darcis, ranked 72nd, will next face the winner of a later match between French fifth seed Julien Benneteau and Luxembourg’s Gilles Muller.

In his 10th pro season, Darcis, 27, seeks his third ATP title after a 2007 triumph in Amersfoort and a 2008 victory in Memphis.

French top seed Gael Monfils withdrew with a right knee injury and was replaced by US lucky loser Blake Strode, who faces Bulgarian Dimitar Kutrovsky in a later second-round match.

Also on the schedule is South African sixth seed Kevin Anderson facing Australian Matthew Ebden with the winner booking a quarter-final date against defending champion Milos Raonic of Canada.