Defending champion Serbia stayed alive in Davis Cup play Saturday with a doubles victory in Belgrade over Argentina. Nenad Zimonjic and Viktor Troicki beat Juan Monaco and Juan Ignacio Chela 7-6 (7-4), 6-4, 6-2 in their semifinals match. Serbia will be counting on U.S. Open champion Novak Djokovic to help pull out a victory on Sunday in reverse singles play. Djokovic withdrew from the opening singles matches on Friday with back pain.