Santiago Giraldo upset second-seeded Tommy Robredo 6-3, 6-4 on Thursday to advance to the quarterfinals of the U.S. Men's Clay Court Championship.
Giraldo will face Alejandro Gonzalez on Friday at River Oaks Country Club. Gonzalez advanced when fifth-seeded Feliciano Lope retired because of severe allergies. Gonzalez led 6-3, 2-0.
Earlier, Donald Young Jr. beat former champion Juan Monaco 6-7 (4), 6-4, 6-3. Young will face fourth-seeded Fernando Verdasco, a 6-0, 4-6, 6-3 winner over Steve Johnson
Jack Sock also won, beating Benjamin Becker 6-4, 6-3. Sock will face the winner of the match between third-seeded Nicolas Almagro and Michael Russell.
On Wednesday, Sam Querrey and Dustin Brown set up a quarterfinal match. Brown beat top-seeded John Isner in three sets.