John Isner lost to Viktor Troicki 7-6 (4), 6-7 (5), 7-5, 6-4 to give Serbia a 1-0 lead over the United States in the first round of the Davis Cup.
Isner had 21 aces in his Davis Cup debut, but Troicki converted his fourth match point with a crosscourt volley after 3 hours, 36 minutes on the clay court at Belgrade Arena.
The American led 5-3 and served for the first set, but lost it in a tiebreaker.
``I usually play better when I win the first set,'' said Isner, who admitted being a bit nervous in his debut. ``I couldn't convert some of my chances and it's a credit to Troicki.''
Sam Querrey will face second-ranked Novak Djokovic in the second singles.
The match marks the first time since 2000 that neither Andy Roddick nor James Blake has played for the U.S. team.
Top-ranked Bob and Mike Bryan will play the Serbian pair of Nenad Zimonjic and Janko Tipsarevic in doubles on Saturday.
The reverse singles wrap up the best-of-five series on Sunday. The winner will play either Croatia or Ecuador in the quarterfinals on July 9-11.
The Americans lead all nations with 32 Davis Cup titles, while Serbia has never progressed beyond the first round in the World Group.
