BELGRADE, Serbia, Sept. 18 (UPI) -- Juan Martin del Potro claimed the decisive point Sunday when world No. 1 Novak Djokovic retired with an injury, putting Argentina into the Davis Cup finals.
Del Porto was up 7-6 (7-5), 3-0 when Djokovic fell to the court and had to be helped to the bench by teammates, ending Serbia's chances of repeating as Davis Cup champion.
That was the third point in the best-of-five Davis Cup semifinals series for Argentina, which moves to the finals Dec. 2-4 against Spain. The Spaniards, who won the Davis Cup in 2008 and 2009, advanced over France with a 4-1 semifinals series.
The series in Spain was marked by the very strong play of world No. 2 Rafael Nadal, who lost to Djokovic finals in a tough four-set match last Monday in the U.S. Open finals.
Nadal showed no signs of fatigue over the weekend but Djokovic, who arrived in Serbia less than 24 hours before the Argentina series began, begged off Friday's singles match. Argentina won both singles Friday but Serbia stayed in contention with a doubles match win Saturday.
It was obvious Djokovic was far from top form Sunday but he kept close in the first set until del Potro took three of the last four points in the tiebreaker. Del Potro broke Djokovic's serve in the second game of the second set and when he sent a shot wide to end the third game, Djokovic fell to the court in pain and couldn't continue.
The severity of the injury was unknown.
Janko Tipsarevic was ahead 6-2 when Argentina's Juan Monaco retired in the final match.