Argentina took a big step towards reaching the Davis Cup final when David Nalbandian and Juan Martin Del Potro secured a 2-0 lead over holders Serbia on Friday.
The home team;s hopes of advancing to their second successive final suffered a huge blow before a ball was hit as world number one Novak Djokovic pulled out of the opening singles rubber with pain in his lower back and ribs.
Djokovic, who won the US Open in New York on Monday, arrived in Serbia less than 24 hours before his scheduled tie with Nalbandian and could not recuperate in time.
Replacement Viktor Troicki was no match for the Argentine who played the kind of tennis that made him the World No 3 in 2006, blowing away his opponent 6-4, 4-6, 6-2, 6-3.
"I was prepared to play either Djokovic or Troicki," Nalbandian told a news conference. "We knew Djokovic might not play because these things can happen in the Davis Cup.
"Either way I think I played really well. The crowd created a great atmosphere out there and I really enjoyed it."
Del Potro then produced a clinical performance against Janko Tipsarevic to win 7-5, 6-3, 6-4 and put the 2008 finalists in the driving seat.
In the other semi-final in Cordoba, Spain also held a 2-0 lead over France.
Now ranked 74th in the world, Nalbandian revived memories of his heyday as he silenced the normally raucous Belgrade crowd.
He hit a staggering 50 winners and scored 25 points more than Tipsarevic who made 58 unforced errors and converted only three of 12 break points.
The 15,000 home fans had little to cheer and the small but vociferous band of Argentine supporters made most of the noise as Del Potro carried on where Nalbandian left off.
Tipsarevic saved three set points on his serve in the 10th game of the opening set but could not repeat the feat in the 12th as Del Potro capitalised on his fifth set point.
With some dejected Serbian fans leaving the upper tiers of the impressive Belgrade Arena, 2009 US Open champion Del Potro put his foot on the gas pedal and raced through the second set after breaking serve in the fourth game.
He hit a superb backhand cross-court winner and then held serve for the rest of the set, much to the delight of his teammates and captain Tito Vasquez who jumped off their seats with joy almost every time he earned a point.
Del Potro conjured a break of serve in the seventh game of the third set and then held his serve with ease to wrap up the match in two hours 32 minutes, ending it with an ace on his second serve.
Nenad Zimonjic and Tipsarevic meet Juan Monaco and Juan Ignacio Chela in Saturday;s doubles, with the reverse singles scheduled for Sunday.