Updated

Houston, TX (SportsNetwork.com) - Third seed Nicolas Almagro of Spain reached the quarterfinals, while fellow countryman Tommy Robredo was sent packing Thursday at the U.S. Men's Clay Court Championship.

Almagro topped American Michael Russell 6-2, 6-3, while an upset came when Santiago Giraldo of Colombia took out Robredo, the No. 2 seed, in 6-3, 6-4 fashion at River Oaks Country Club.

The 28-year-old Almagro was last year's Houston runner-up to John Isner.

Meanwhile, fourth-seeded Spanish left-hander Fernando Verdasco got past American two-time NCAA singles champion Steve Johnson 6-0, 4-6, 6-3, Colombian qualifier Alejandro Gonzalez was leading another Spanish lefty, Feliciano Lopez, 6-3, 2-0, when the fifth seed retired, and American southpaw Donald Young upended sixth-seeded Argentine Juan Monaco 6-7 (4-7), 6-4, 6-3. Monaco titled here two years ago. Verdasco and Young will battle on Friday.

Also on Day 4, American Jack Sock erased German Benjamin Becker 6-4, 6-3.

The 2014 Houston champ will claim $85,900.