The top seeded Andy Roddick of USA survived a scare from Ivo Karlovic of Croatia and he defeated his opponent in straight sets by 7-6 (7/4), 7-6 (7/5) to advance in to semifinals of the Washington Classic tournament on Friday.

The fifth ranked Roddick connected 74 percent of first serves in the match as compared to 59 percents by his opponent. However, Karlovic smashed 13 aces as compared to only seven aces by Roddick.

Roddick will meet with John Isner in the semifinal. John ousted eighth seeded Tomas Berdych of Czech in a three setter match by 6-3, 6-7 (10/12), 6-2. Roddick and John had met each other only once in the past.

In other semifinal of the tournament, the defending champion Juan Martin Del Potro of Argentina will lock horns with fourth seeded Fernando Gonzalez of Chile. Gonzalez defeated Tommy Haas 7-5, 6-4 while Del Potro was declared winner of the match when fifth seeded Robin Soderling of Sweden pulled himself out of the quarterfinal match due to a right elbow injury.