World number five Juan Martin del Potro has booked his place in the semi-finals of the Sydney International Tennis tournament. In Sydney on Thursday, the Argentine defeated Czech Davis Cup hero Radek Stepanek in three sets 6-4 3-6 6-3. Top seed Del Potro has now set up a last-four clash against Russian Dmitry Tursunov, who advanced with a 7-6 6-2 win against Uzbek Denis Istomin.Bernard Tomic and Marinko Matosevic could set up an all-Australian semi-final if the pair win their quarter-finals later today. Defending champion Tomic takes on Ukrainian Alexandr Dolgopolov while wildcard Matosevic plays qualifier Sergiy Stakhovsky.