Six-time champion Roger Federer rallied past Juan Martin del Potro 4-6, 7-6 (2), 7-5 Saturday, setting up a semifinal against Rafael Nadal at the ATP World Tour Finals. Novak Djokovic will take on Stanislas Wawrinka in the other semifinal Sunday at the year-end tournament. Federer and del Potro needed a win their final round-robin match to progress from Group B. They treated the crowd to a tense and entertaining match, with Federer trailing in all three sets. More...