MOSCOW —An ailing Novak Djokovic retired despite leading in the first reverse singles match today, giving Russia a 3-2 win over Serbia and a spot in the Davis Cup quarterfinals.

Djokovic, who was playing his first singles match since winning the Australian Open, was leading Nikolay Davydenko 6-4, 6-3, 4-6 when he quit, allowing Russia to take an insurmountable 3-1 lead.

Djokovic withdrew from the opening singles Friday because of flu symptoms but paired with Nenad Zimonjic on Saturday to give Serbia a point by beating Mikhail Youzhny and Dmitry Tursunov in straight sets.

"I decided to stop because I don't want to risk my health," Djokovic said. "I wanted to fight, I tried to play but in the end I was aware of the fact that I am very dizzy and I have a lack of energy. I just didn't want to continue because of the risk I had."

In the final match, Davis Cup rookie Viktor Troicki beat Dmitry Tursunov 7-6 (7), 6-4, 6-3 to give Serbia its second point.