Defending champions Serbia slipped 2-0 down to Argentina in their Davis Cup semi-final on Friday, failing to recover from the absence of world number one Novak Djokovic, who pulled out of the opening day through injury and fatigue.
David Nalbandian defeated Victor Troicki, who replaced Djokovic, 6-4, 4-6, 6-2, 6-3 before former US Open winner Juan Martin Del Potro eased past Janko Tipsarevic 7-5, 6-3, 6-4, his third career win over the Serb.
Djokovic was suffering from fatigue as well as a back injury picked up in his US Open final win over Rafael Nadal on Monday.
In front of 15,000 fans at the Belgrade Arena, world number 74 Nalbandian took full advantage to see off Troicki, who won the decisive leg of last year's final against France.
"I played OK but not good enough to beat Nalbandian," said Troicki. "I was lacking confidence because I had some bad tournaments coming into this match. I felt ready physically but didn't feel good on the court.
"I didn't feel any pressure playing instead of Novak becase we knew of the situation for a few days."
Nalbandian said he only knew of Djokovic's absence 30 minutes before the match started.
"But I knew yesterday that I had to be prepared to play anyone. We are well-prepared, in good form and ready to write history."
World number 16 Troicki broke Nalbandian in the third game of the opening set but the Argentine hit back in the sixth and ninth games before taking the first set.
Troicki broke in the ninth game of the second set to level the rubber.
But Nalbandian then raced through the third and fourth sets to seal victory in 2 hours and 51 minutes.
The winners of the semi-final will face either Spain or France in the final.
Spain were leading 2-0 in Cordoba at the end of the first day.