Federer Defeats Del Potro to Set Up Match With Nadal Roger Federer rallied past Juan Martín del Potro, 4-6, 7-6 (2), 7-5, on Saturday, setting up a semifinal against Rafael Nadal at the ATP World Tour Finals in London. Novak Djokovic will take on Stanislas Wawrinka in the other semifinal Sunday at the year-end tournament. In doubles, the top-ranked team of Bob and Mike Bryan booked a spot in the semifinals by defeating the veteran Polish duo of Mariusz Fyrstenberg and Marcin Matkowski, 4-6, 6-3, 10-5.