Tennis: Serbia out as Djokovic retires

Novak Djokovic collapses in a heap before retiring injured in his Davis Cup rubber against Juan Martin Del Potro

STORY HIGHLIGHTS

• Holders Serbia exit Davis Cup at semifinal stage to Argentina
• Serbia's World No.1 Novak Djokovic retires from his rubber against Juan Martin Del Potro
• Del Potro's win gives Argentina winning 3-1 lead in Belgrade
• Rafael Nadal secures Spain's passage to the final as he beats Jo-Wilfried Tsonga

(CNN) -- Davis Cup holders Serbia exited this year's competition as their world number one Novak Djokovic was forced to retire from his crucial rubber against Juan Martin Del Potro with a back injury.
Djokovic, who sat out the opening round of singles matches, was trailing a set and 3-0 when he called it a day in front of a partisan home crowd in the Belgrade Arena.
Del Potro's victory gave Argentina an unbeatable 3-1 lead in the tie, ending home hopes after Nenad Zimonjic and Viktor Troicki had pulled Serbia back into contention with their doubles victory Saturday.
They will play Spain in the final after Rafael Nadal gave them a winning 3-1 lead over France with a crushing straight sets win over Jo-Wilfried Tsonga on the clay in Cordoba.

I am not angry, just sad and disappointed, as I really believed I could endure the match and win it
Novak Djokovic

France, like Serbia, had won the doubles rubber to trail 2-1, but Nadal, beaten by Djokovic in the U.S. Open final last week, showed no signs of fatigue with a 6-0 6-2 6-4 victory.
It was the second success of the weekend for Nadal, who beat Richard Gasquet in the opening singles matches, backed up by David Ferrer's win over Gilles Simon.
Tsonga, who beat Nadal at Queen's Club earlier this year, was no match for the world number two on his favorite surface and despite a brief rally in the third set was beaten in a little over two hours.
Gasquet was to play Fernando Verdasco in the final dead rubber. The victory avenged Spain's 5-0 whitewash by France in last year's quarterfinals.
France went on to reach the final where they were beaten by a resurgent Serbia in the final, with Djokovic leading the way as he embarked on his incredible unbeaten run and victory in three of this year's four grand slams.
But Sunday saw one of his few setbacks in 2011, visibly struggling after losing a tight first set tiebreak 7-5. 2009 U.S Open champion Del Potro showed no mercy and quickly broke at the start of the second to take control.
Djokovic, who had needed treatment for his back while beating Nadal at Flushing Meadows, admitted after his defeat that he had taken a risk in attempting to lift his country back into the tie.
"I was not even 60 percent ready, but we have accepted that risk although we knew that my injury could worsen," he told the official Davis Cup website.
"I am not angry, just sad and disappointed, as I really believed I could endure the match and win it, but against a player who pulled in 80 percent of his first serve, that was impossible," Djokovic added.
He will now have further tests to examine the extent of his injury ahead of lucrative end of year tournaments which culminate in the ATP Tour Finals in London.
Meanwhile, Argentina will travel to Spain for December's final in a repeat of the 2008 title match which the Spanish won in Mar del Plata.