Top-seeded Nicolas Almagro of Spain defeated Italian Paolo Lorenzo 6-4, 6-4 on Friday to advance to the U.S. Men's Clay Court semifinals.
Fifth-seeded American John Isner also advanced, hitting 19 aces to overpower Lithuania's Ricardas Berankis 6-3, 3-6, 6-3.
Almagro, ranked 12th in the world, will next face American wild card Rhyne Williams, who rallied from an 0-3 deficit in the third set to beat Spain's Ruben Ramirez Hidalgo, 7-6 (1), 1-6, 6-4.
Third-seeded Juan Monaco of Argentina, the defending champion, defeated American Robby Ginepri 6-1, 6-0 in the other quarterfinal.
Almagro and Lorenzo stayed on serve in the first set until the final game, when Lorenzo double-faulted to start the game and then hit a drop shot that fell short on the first break point.
After trading breaks early in the second set, Almagro won the match with a forehand winner that left his opponent flat-footed.
"I played better than yesterday, but I feel I can do a little bit better and I will look for that," Almagro said. "I want to get to the final, but I know that match will be tough. I need to be ready to fight for every point."
The 6-foot-9-inch (2.05 meter) Isner dominated his 5-foot-9 (1.75 m) opponent in the first set, but Berankis fought back to take the second set, breaking Isner in the eighth game. Isner had 10 aces in the third set, two on the final two points, and made 90 percent of his first-serve points.
"I felt when the rally went past five balls, it didn't look really good for me," Isner said. "I tried to keep the points shorter, especially on my serve and I did that exceptionally well except for one game."
The 22-year-old Williams, ranked 144th in the world, won the first set after sailing through a runaway tiebreaker, but was let down by his serve in the second set and allowed the Spaniard to level the match.
Hidalgo saved two match points to hold his serve in the ninth game of the third set, but Williams served a love final game to win the match, ending it with consecutive aces.
"I was really worn out after the first set," Williams said. "We played some brutal points. It was an hour long, pretty physical."