Belgrade, Sep 16: U.S. Open champion Novak Djokovic pulled out of Serbia's opening singles match against David Nalbandian of Argentina on Friday in the Davis Cup semifinals because of back pain.
Viktor Troicki took the place of Djokovic, who returned to Serbia on Thursday after beating Rafael Nadal on Monday in the U.S. Open final.
The top-ranked Djokovic also pulled out of Serbia's opening match of the semifinals last year against the Czech Republic because he needed rest after the U.S. Open, where he lost to Nadal in the final. Troicki was also a late replacement for Serbia on the opening day last year while Djokovic played the reverse singles.
Djokovic led Serbia to its first Davis Cup title last year.
In Friday's other singles match, Janko Tipsarevic is to face Juan Martin del Potro. AP
