It took more than four hours, but Roger Federer was able to eke out a win against Juan Martin Del Potro of Argentina in their semifinal match on Friday. Federer won the three set match 3-6, 7-6, 19-17. The Swiss tennis star had several opportunities to close it out earlier, serving at 10-9 in the third set, but Del Potro held on to break Federer. Both players appeared nervous, hitting easy volleys into the net and sending shots long at crucial moments. Federer, who has won 17 Grand Slam tourneys but not an individual Olympic gold medal, will next face the winner of the semifinal between Andy Murray and Novak Djokovic.