Without Djokovic, Argentina leads Serbia 2-0

In the absence of Novak Djokovic, defending champion Serbia lost both its matches Friday to trail Argentina 2-0 in the Davis Cup semifinals.

Argentina's David Nalbandian beat Viktor Troicki 6-4, 4-6, 6-2, 6-3, and Juan Martin del Potro topped Janko Tipsarevic 7-5, 6-3, 6-4.

Djokovic pulled out of the opening singles because of back pain, four days after beating Rafael Nadal in the U.S Open final. He was replaced by Troicki.

Nalbandian had little trouble against his replacement, who had 58 unforced errors at an indoor hard court in Belgrade Arena.