Former champion Radek Stepanek was a round upset victim Thursday at the $531,000 SAP Open.

Belgian Steve Darcis bounced the fourth-seeded Czech 7-6 (7-4), 7-6 (7-2) on the hardcourts at HP Pavilion.

The world No. 29 Stepanek reached back-to-back finals here in 2008 and 2009, with his title coming in '09.

Fifth-seeded South African Kevin Anderson took down Australian Matthew Ebden, 6-1, 6-2, and will meet defending champion Milos Raonic of Canada in Friday's quarterfinals.

Frenchman Julien Benneteau, the sixth seed, had little trouble with Gilles Muller of Luxembourg, 6-2, 6-4, and will square off against Darcis on Friday.

Bulgarian qualifier Dimitar Kutrovsky topped American lucky-loser Blake Strode 7-5, 6-3 on Day 4. Strode joined the draw Wednesday when top seed Gael Monfils of France pulled out with an injury.

In other unseeded action, American Ryan Harrison took down compatriot Robby Ginepri, 6-3, 2-6, 7-6 (7-0), while Denis Istomin of Uzbekistan defeated American Michael Russell, 6-2, 6-2, in the final match of the day.

Harrison will face Kutrovsky in the quarterfinals and Istomin will take on three-time San Jose winner Andy Roddick on Friday.

This week's SAP Open champion will earn $95,860.