Tomas Berdych and Radek Stepanek defeated Nenad Zimonjic and Ilija Bozoljac 6-2, 6-4, 7-6 (4) on the indoor hard-court at Belgrade Arena. The victory improved the Czech pair's impressive cup doubles record to 14-1.
Berdych plays Novak Djokovic, on a 23-match winning run, in the first reverse singles on Sunday, and the final could be decided when Stepanek likely meets cup rookie Dusan Lajovic in the final rubber.
"I am in the best possible position after Saturday," said Berdych, who has beaten Djokovic only twice in 16 encounters, and never on a hard court. "I have nothing to lose. I am going to go there and fight for each point."
Serbia captain Bogdan Obradovic said Zimonjic and Bozoljac gave their best, but lost against a better pair.
"But we were in similar situations before," Obradovic said.
Serbia came from 2-1 down in the 2010 cup final against France, and in this year's semifinals against Canada.
But both heroes of those ties aren't playing. Viktor Troicki, who clinched Serbia's only cup title in 2010, is serving a doping ban, and Janko Tipsarevic, who secured the win over Canada, is sidelined by a heel injury.
Obradovic said he was not sure if Lajovic, who lost against Berdych in straight sets on Friday, would play if there's a fifth rubber.
On Saturday, the Czechs broke Zimonjic at the start of the first two sets. Zimonjic netted an easy volley in the second set to give the Czechs a commanding two-set lead.
Stepanek played almost faultlessly. He saved the only break point for the Serbs at 2-3 in the third set with a neat drop shot. In the third-set tiebraker, Stepanek first lost his serve, but then Zimonjic and Bozoljac both suffered mini-breaks. Stepanek won the match with an ace.
"Today, it worked out really well. We fit perfectly. Honestly," Stepanek said. "It was one of the best matches we played. But, we have to stay humble, focused and concentrated.
"If it comes down to the fifth match, I will be ready to fight to the last point."
Zimonjic said "they were better in every aspect of the game."
"We had a little chance in the third set, but that was the only one. They were controlling the match from the beginning to the end."
AP writer Jovana Gec contributed.