Top seed Andy Roddick [Images] overcame a 29-ace performance by Ivo Karlovic [Images] and advanced to the semi-finals of the Washington Classic with a 6-7, 7-5, 6-4 victory Friday.

In a match-up of two of the game's top power players, Roddick scored the decisive service break in the ninth game of the final set when Karlovic opened with two double faults.

The 6-foot-10 Croatian dug himself into a love-40 hole and Roddick took the game two points later to grab a 5-4 lead. Roddick, who had 19 aces, easily served out the match.

Roddick will face 13th seed Paradorn Srichaphan [Images] of Thailand in one of the semi-finals on Saturday. Paradorn, a finalist here in 2002, advanced with a 6-4, 7-5 victory over Peru's Luis Horna.

In the other semi-final, 2002 Washington champion James Blake [Images] will face 10th seeded Tomas Berdych of the Czech Republic. The unseeded Blake beat France's [Images] Arnaud Clement [Images] 6-3, 6-2, while Berdych edged American Bobby Reynolds 7-6, 7-6.

The heat exceeded 38 degrees Celsius (100 Fahrenheit) on court and sapped Karlovic's energy as his match against Roddick progressed.

"He was serving at 80 percent first serve but it felt a lot more like 90 percent," said Roddick. "Not a lot you can do. I kept telling myself to hold on.

"He started getting a little tired in the third set. His service percentage dropped a lot so I was getting some looks at second serves."

FIFTEEN ACES

Karlovic had 15 aces in the opening set, eight in the second, but managed only six in the third. His first-serve percentage fell to 52 percent in the final two sets, down from 75 percent in set one.

There were few rallies in the two-hour match with both players' serves dominant. Roddick never faced a break point while Karlovic was broken twice.

"It wasn't a whole lot of fun for a little while there," said Roddick. "It was like watching paint dry."

The 75th-ranked Karlovic won the first-set tiebreak 9-7 when Roddick double-faulted on the final point. Karlovic lost his serve at 15 in the pivotal 11th game of the second set, paving the way for the winner-take-all final set.

Karlovic admitted the heat had taken its toll.

"It was hot out there and I was having trouble breathing and moving," he said.

The fifth-ranked Roddick has one of the most feared serves on the circuit but conceded Karlovic's is better.

"I won't say this often but I don't think my serve compares to his serve," said Roddick. "You can get a racket on my serve. I don't think you'll find a person who says my serve is better than his."

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