Juan Martin del Potro's injury-enforced withdrawal as Argentina's spearhead looks set to leave the Czech Republic hosting defending champion Spain in the Davis Cup final in November.
Both teams led their semifinals 2-1 after the doubles on Saturday.
Czech stalwarts Tomas Berdych and Radek Stepanek won in straight sets in Buenos Aires for a lead that became all the more pivotal when del Potro was ruled out of the reverse singles on Sunday because he aggravated a left wrist injury in his singles win on Friday. In del Potro's place stepped Carlos Berlocq, who made his cup debut in the doubles.
By beating Berlocq, Berdych, who has 35 wins in 22 ties, can clinch the Czech's first home final in 32 years and hand Argentina a first loss in a home tie on clay since 1998.
Not so crucial for Spain in Gijon was losing the doubles to the United States.
Bob and Mike Bryan, one of the greatest pairs in tennis history, duly won their match, but merely delayed by a day a Spain victory regarded as inevitable.
The fifth-ranked David Ferrer is 15-0 on clay, and he also has a winning record against U.S. No. 1 John Isner, who lost a five-setter to Nicolas Almagro on Friday. Almagro was drawn to play decided underdog Sam Querrey in the last match.
With a Ferrer win, Spain will owe a visit to the Czech Republic, having humbled the Czechs 5-0 in Barcelona in the 2009 final.
The final would be Spain's fourth in five years. By then, Marcel Granollers and Marc Lopez should be over left calf injuries.
Lopez hurt his in reaching the U.S. Open semifinals a week before with Granollers, who strained his in the second set against the Bryans.
Granollers looked so bad that even captain Alex Corretja said, "I definitely would have retired."
But Granollers persevered, and was picked apart by the Bryans, who won 6-3, 3-6, 7-5, 7-5 in 3 hours, 38 minutes.
"It was a battle," Bob Bryan said after the twins kept the U.S. from losing a tie for the fifth time in their cup careers. "We came here to get a win, we kept the team alive. It wasn't pretty all the time but a win's a win and we're happy with that."
Berdych and Stepanek were even more remorseless in beating Berlocq and Eduardo Schwank 6-3, 6-4, 6-3. The Czechs have yet to drop a set in three cup doubles this year.
Playing a third straight day doesn't faze Berdych - he's done it six times in his cup career, most recently in the quarterfinal win over Serbia in which he won all three of his matches.
"My physical aspect is fine," he said. "I won two tough matches, but I'm here to be ready for three days. Winning two matches gives me a lot of confidence."
That confidence would have only grown after learning del Potro, against whom he had a losing record, withdrew from the tie.
Del Potro hurt his left wrist in the U.S. Open quarterfinals, and was warned after then he had to rest it for two weeks. But patriotism drove the Olympic bronze medallist to play and beat Stepanek on Friday. He won without his double-handed backhand but enflamed the wrist and team doctor wouldn't let him continue to risk it any further.
He has to rest it for 10 days.
Captain Martin Jaite said he learned late Friday that del Potro would not play again, but said he didn't tell the team until after Saturday's doubles.
"It was not what the team expected, but we're OK and we have two more matches," he said. "Obviously it's a blow to the team, but we'll continue to fight for it."