HOUSTON (AP) 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 at River Oaks Country Club.
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.
The 24-year-old Young has won consecutive matches on clay for the first time in an ATP World Tour event.
''Definitely the biggest win for me, (beating) a former top-10 guy who wins most of his matches on clay,'' Young said. ''Happy to move through, to be honest. I'm competing well and my shots are falling. I'm feeling good and confident.''
Monaco, the 2012 winner, said he was bothered by a sore shoulder but praised Young's play.
''He was strong today,'' Monaco said. ''He deserved to win.''
Monaco missed the last three months of the 2013 season because of a strained wrist.