Top seed Andy Roddick and American rookie John Isner have reached the semifinals of the Legg Mason Tennis Classic hard court tournament here in Washington. As VOA's David Byrd reports, Roddick faces Ivo Karlovic of Croatia while Isner plays France's Gael Monfils.

Andy Roddick returns a shot against Hyung-Taik Lee of South Korea during a match in the Legg Mason Tennis Classic, 3 Aug. 2007

In the semifinals, Roddick plays Ivo Karlovic of Croatia, who scored a three-set win over Paul Capdeville of Chile, 4-6, 6-3, 7-6. Roddick says that playing Karlovic is always a challenge.

"With him it is difficult because some times you can play well and lose and sometimes you can play badly and win," he explained.  "With a guy who has a weapon like him, and his serve, it is a little bit of a crap shoot sometimes.  I think you just have to be mentally ready when and if you get a chance."

All-time, Roddick has a 2-1 record against Karlovic.

Isner, whose first professional match was less than a month ago, fired 30 aces and 23 service winners to beat German Tommy Haas in three sets, 6-4, 6-7, 7-6. The American, who stands two meters, five centimeters tall, says he is enjoying the tournament.

"To tell you the truth, I am not that nervous out there because I know no matter what I have nothing to lose out there," he said.  "If I go down 7-6 in the third, then I lost 7-6 in the third to the number 10 player in the world or whatever. So I am just enjoying the moment."

In Saturday's semifinals, Isner will play Frenchman Gael Monfils, who ousted third seeded Marat Safin of Russia in straight sets, 6-3, 7-5.

The tournament is part of the U.S. Open series, a string of events players are using to prepare for the last major tournament of the year, the U.S. Open, which starts later this month in Flushing Meadows, New York.