(CNN) -- Bob and Mike Bryan kept U.S. hopes alive in their Davis Cup semifinal against Spain in Gijon on Saturday with a hard-fought victory over Marcel Granollers and Marc Lopez.
The world No.1 pairing ran out 6-3, 3-6, 7-5, 7-5 winners to record their 20th Davis Cup win in three hours 38 minutes.
The result means the match score is now 2-1 in the host's favor heading into Sunday's singles matches, and U.S. captain Jim Courier concedes his team face a daunting challenge against the defending champions.
David Ferrer will play John Isner in the first reverse singles match with Nicolas Almagro taking on Sam Querrey in the second match, if required.
"Ferrer is such a warrior and a great competitor and John's going to have to play better than he did yesterday to stand a chance. He's a little bit more physically taxed than David is for sure," Courier said.
Spain, who are without the injured Rafael Nadal, are bidding to reach a sixth final in 10 years.
In the other semifinal, Argentina's hopes of winning a first Davis Cup suffered a setback in Buenos Aires as Tomas Berdych and Radek Stepanek of the Czech Republic beat Carlos Berlocq and Eduardo Schwank in the doubles match on Saturday.
The Czech pair coasted to a 6-3 6-4 6-3 victory in two hours 37 minutes to stun the home crowd at the Parque Roca stadium.
"It's very loud in here and we knew that when we were coming to this place. It was always going to be like that so we concentrated only on our half of the court," Stepanek said.
The Czechs, who are looking for a first win in the competition for 32 years, will take a 2-1 lead going into Sunday's deciding singles where Argentina will be without Juan Martin del Potro.
Team captain Martin Jaite said the world No.8's niggling wrist injury has forced his withdrawal.
Del Potro's replacement, Carlos Berlocq will face Berdych in the opening singles match, with Stepanek up against Juan Monaco in the second.