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 timeout. Querrey led 4-1 and wasted four set points at 5-4.
Djokovic needed five match points to win, converting with a forehand drive after 3 hours, 21 minutes.
"Querrey played better and better as the match progressed and he gave me a lot of trouble,'' Djokovic said. "Despite our big 2-0 lead, nothing is decided yet.''
Querrey was satisfied with his performance.
"Despite the score, it was a very tight match,'' he said. "I was trying to get him on the move instead of him dictating.''
Isner, making his cup debut, hit 21 aces but Troicki converted his fourth match point with a crosscourt volley after 3 hours, 36 minutes.
"It was tough, but this win gives us a great chance to get to the quarterfinals,'' Troicki said.
Isner led Troicki 5-3 and served for the first set, but lost it in a tiebreaker. Troicki said he gained confidence after taking the first set.
"I usually play better when I win the first set,'' Isner said, admitting he was a bit nervous. "I couldn't convert some of my chances and it's a credit to Troicki.''
Saturday's doubles features top-ranked Bob and Mike Bryan against Nenad Zimonjic and Janko Tipsarevic on the indoor claycourt in Belgrade Arena.
Serbia is trying to pass the first round in the World Group for the first time.
It's the first time since 2000 that neither Andy Roddick nor James Blake were on the U.S. team.
The winner will play either Croatia or Ecuador in the quarterfinals July 9-11.
