Argentina beat holders Serbia 3-2 in their Davis Cup tennis semi-final after world number one Novak Djokovic retired with a rib and lower back injury against Juan Martin Del Potro.
Del Potro was leading 7-6 3-0 when Djokovic fell to the ground with a scream of pain and then retired, giving Argentina an unassailable 3-1 lead before Janko Tipsarevic beat David Nalbandian in the dead rubber.
After he was helped to the bench by captain Bogdan Obradovic and his team mates, a tearful Djokovic embraced Del Potro and received a standing ovation from the 18,000 home crowd in the Belgrade Arena.
The Serbian star told a news conference he was bitterly disappointed to end the tie due to injury, but explained he was only 60 percent fit going into the match and played on despite the risk of aggravating the injury which he first felt at the US Open.
Games went with serve in a tense first set with no break points on either side.
Del Potro clinched the set after winning three of the last four points in the tie break.
Clearly lacking the spark that took him to three grand slams and seven other tournament wins this season, Djokovic showed signs of nerves after making a flurry of unforced errors in front of a supportive home crowd.
Del Potro finally broke the Serb's serve in the second game of the second set and was in complete control when Djokovic decided he could not carry on.
Three-times runners-up Argentina will play Spain in the final after the 2009 champions won both reverse singles to complete their 4-1 win over France.