Donald Young Jr. beat former champion Juan Monaco 6-7 (4), 6-4, 6-3 on Thursday to advance to the quarterfinals of the U.S. Men's Clay Court Championship.
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.
Alejandro Gonzalez advanced when fifth-seeded Feliciano Lope retired because of severe allergies. Gonzalez led 6-3, 2-0. Gonzalez will face the winner of a match between second-seeded Tommy Robredo and Santiago Giraldo.
On Wednesday, Sam Querrey and Dustin Brown set up a quarterfinal match.