Novak Djokovic struggled past Sam Querrey 6-2, 7-6 (4), 2-6, 6-3 for Serbia to take a 2-0 lead against the United States in their Davis Cup first-round tie on Friday. In the opening singles, Serbia's Viktor Troicki beat John Isner 7-6 (4), 6-7 (5), 7-5, 6-4. Second-ranked Djokovic began having problems in the second set, smashing his racket and asking for a medical. More...