Roddick in last four

August 08, 2009 Top seed Andy Roddick continued his fine form with a straight-sets win over fellow big server Ivo Karlovic to reach the semi-finals in Washington.The American came through 7-6 (7-4) 7-6(7-5) to set up a clash with compatriot John Isner at the Legg Mason Classic. Isner, another huge server, defeated eighth seed Tomas Berdych 6-3 6-7 (10-12) 6-2. Second seed and defending champion Juan Martin del Potro will face fourth seed Fernando Gonzalez in the second semi. Argentine Del Potro progressed without hitting a ball after fifth seed Robin Soderling was forced to withdraw because of a right elbow problem.