Washington:Andy Roddick defeated big-hitting Ivo Karlovic in two tiebreaker sets on Friday to reach the semifinals of the Legg Mason Classic.
Top-seeded Roddick won 7-6 (4), 7-6 (5), with the typical scoreline for two big servers disguising the repeated service breaks.
Roddick's semifinal opponent will be American compatriot John Isner, who upset eighth-seeded Czech Tomas Berdych 6-3, 6-7 (10), 6-2.
In other quarterfinals, fourth-seeded Fernando Gonzalez defeated Tommy Haas 7-5, 6-4, setting up a semi against second-seeded defending champion Juan Martin del Potro, who advanced after Robin Soderling withdrew before their match with a right elbow injury.
Playing in his first tournament since losing in an epic Wimbledon final, Roddick is two wins away from his fourth Washington title after overcoming the first two breaks of his serve in six career matches against the 2.05-meter (6-foot-10) Karlovic.
Roddick entered the match with a 4-1 record against the Croatian, who leads the ATP Tour in aces with Roddick one spot behind. Their six previous sets had gone all the way to a tiebreaker, a trend that held in this match, even with both players broke the other's serve twice.
After netting a volley to go down 1-3 in the first, Roddick broke back to get it to 3-4. The action moved to that inevitable tiebreaker, which the American took control of by winning the first three points.
In the second set, Karlovic broke in the opening game, with Roddick hitting a ball out of the stadium in frustration.
His composure returned and after earning his second break, Roddick lost only five more points on his serve the rest of the way, while earning a mini-break to go up 4-3 in the tiebreaker.
"Being down an early break against Karlovic is a recipe for disaster," said Roddick, who has an ATP-best 29-6 record in tiebreakers this year. "I consider myself fortunate to get out it of it one time, much less two times."
Asked why Roddick has got the better end of tiebreakers between the two, including winning the past six, Karlovic said, "Luck, it's as simple as that."
Gonzalez too is playing in his first event since Wimbledon. Tied at 5-5 in the first set, he angled a forehand past the charging Haas for the first break point of the match. He then had three forehand winners in his own service game to close out the set.
"Both of us played really good tennis in the beginning," said Gonzalez, who has been dealing with right knee tendinitis. "I only had one break point and I did it. That gave me a lot of confidence for the rest of the match."
Gonzalez broke serve to open the second set and again to go up 5-2 against a frustrated Haas. A Wimbledon semifinalist this year, Haas broke back and then held his serve to get to 5-4. But the 11th-ranked Gonzalez, who made the final here in 2003, rebounded and put away an overhead smash to win the match and the Chilean improved to 5-0 in quarterfinals this year.
Isner, who reached the final in 2007 as a qualifier before losing to Roddick, set up another chance by beating Berdych in their first head-to-head meeting.
The 80th-ranked American, who had 17 aces, served for the match at 5-4 in the second set, and then couldn't convert three match points in the tiebreaker. Isner rebounded to break Berdych twice in the final set.
Soderling, a finalist at the French Open, was expected to have his elbow scanned on Friday.
"My elbow started to bother me two weeks ago and this morning it was really sore," the Swede said, adding that he hopes to play one or two tournaments before the U.S. Open.