Mike and Bob Bryan continued to be America's most reliable Davis Cup formula as the brothers won their doubles point to trim Spain's lead in their semi-final to 2-1 on Saturday.
The twins were stretched by Marcel Granollers and Marc Lopez in a 6-3, 3-6, 7-5, 7-5 victory in which Granollers was hampered by a left calf injury picked up in the second set.
Granollers stayed in the match but Spain lost momentum and mobility as the Bryans kept alive the visitors' chances of reaching November's final in front of a near capacity 15,000 spectators at the purpose-built venue in the Asturian coastal city.
"It was a battle," Bob Bryan said after the brothers kept the U.S. from losing a tie for the fifth time. "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."
David Ferrer can clinch Spain's fourth trip to the final in five years on Sunday when he faces John Isner in reverse singles, with the fifth-ranked Spaniard 15-0 on clay in the competition. The defending champions have won all previous 37 ties when they have swept the opening singles.
The US has only once recovered from a 0-2 deficit - in 1934 - but its record improves when down 1-2, having done it five times with the last being in 2000.
"These guys did a great job and I'm sure Spain's ready to put us away," US captain Jim Courier said, "but we've two guys ready to fire tomorrow so we'll take our chances and see what happens."
Mike Bryan stumbled chasing down a drop shot to miss out on the first match point, but Lopez provided the US with it on the second opportunity as he double-faulted.
"It's a shame because we felt really good today," said Lopez before alluding to his own calf problem that forced him to retire from the US Open doubles semi-final. "It happened to me in the US one week ago, it's tough."
The Bryans took the opening set before Spain bounced back with an early break in the second set for a lead it would not relinquish despite a marathon third game that appeared to take its toll on Granollers, who limped off to have his calf treated.
"I felt the pinch in my calf, and in the third set I thought I wasn't going to make it," Granollers said. "I fought to the end anyway, but it wasn't enough."
Despite captain Alex Corretja calling on him to retire rather than risk injury, Granollers continued and eventually improved as Lopez carried the hosts through the opening sets. Lopez also sported a bandage on his own left calf.
"It wasn't easy to play a guy that was potentially injured," Mike Bryan said after the 3-hour, 38-minute match. "I thought we played safe for a set and a half."
The Bryans managed to rally each time Spain seemed to gain an advantage and focused their attack on Granollers, and his discomfort and erratic groundstrokes proved costly as he netted many of Spain's 74 unforced errors.
Should Isner beat the fifth-ranked Ferrer, Sam Querrey and Nicolas Almagro are scheduled to play for the final singles point.
Almagro edged Isner in a five-set thriller on Friday to bring his and Ferrer's record on clay in the competition to a combined 23-1.
The winner plays either Argentina or the Czech Republic in November's final.