Novak Djokovic withdrew from his match because of back pain, giving Argentina an insurmountable 3-1 lead over Serbia to reach the Davis Cup final. The top-ranked Serb fell to the floor Sunday with back pain during the third game of the second set after losing the first set to Juan Martin del Potro 7-6 (5). Argentina will play Spain in the final. Rafael Nadal put Spain into the final after routing Jo-Wilfried Tsonga 6-0, 6-2, 6-4 for an insurmountable 3-1 lead against France in the other semifinal. Read more: http://espn.go.com/tennis/story/_/id/6988715/argentina-davis-cup-final-novak-djokovic-withdraws