Three-time champion Andy Roddick defeated bullet-serving Ivo Karlovic 7-6, 7-6 on Friday to book a spot in the semi-finals of the Washington Classic.
Roddick won the tiebreakers 7-4 and 7-5 to set up an all-American affair with John Isner, who beat Czech Tomas Berdych 6-3, 6-7, 6-2 at the $1.4 million hardcourt event.
Fernando Gonzalez knocked out Tommy Haas of Germany 7-5, 6-4 and will face holder Juan Martin Del Potro, who progressed to the last four when Robin Soderling withdrew with an elbow injury.
Roddick weathered 13 Karlovic aces on the way to his fifth win against the Croatian in a match featuring unusually long rallies for two of the hardest-hitters in the game.
The 26-year-old American said the unseasonably cool weather in Washington on Friday evening may have made the court slower.
"The ball felt a little dead," said top-seeded Roddick, playing his first tournament since losing to Roger Federer in an epic five-set final at Wimbledon last month.
"It seems to be playing quicker in the day than at night. We haven't gotten the typical Washington heat yet. I think that's on tap for the weekend."
Having never previously broken Roddick's serve, 30-year-old Karlovic went up a service break in each set, but Roddick battled back both times to force a tie-breaker.
"If you would have told me I'd break him twice, I would have thought it would have been a lot more comfortable than the end score," said Roddick, who managed only seven aces against Karlovic.
Gonzalez needed an hour and 23 minutes to subdue the 10th-seeded Haas, who was bidding to reach his fourth successive semi-final.
"He was hitting the ball pretty hard from the forehand side," said Haas. "He is a very tough player to face. It is really hard to do anything when he starts hitting forehands."
Gonzalez, 29, scored the only service break of the opening set in the 11th game before serving it out.
The Chilean then broke the 31-year-old German twice to take a 5-2 second-set lead before securing the win, his third in four hit-outs with Haas.
"I lost focus during a couple of games in the match and dropped serve a few times which probably made the difference," said Haas.
