Gijon - Defending champions Spain took a leap towards a fourth Davis Cup final in five years when clay-court masters David Ferrer and Nicolas Almagro opened a 2-0 semi-final lead over the United States on Friday.
Ferrer beat Sam Querrey 4-6, 6-2, 6-2, 6-4 in the opening singles rubber on Spain's red clay in three hours.
Almagro then triumphed in a four-hour slog against John Isner, winning 6-4, 4-6, 6-4, 3-6, 7-5.
If Spain's doubles team of Marcel Granollers and Marc Lopez beat the American twins Bob and Mike Bryan on Saturday, the five-time champions will be through to the final to defend their title.
Ferrer lost his first set to Querrey but tamed the gangly American's blistering forehand with deft returns to the delight of the rowdy crowd.
"It was a hard match, difficult at every moment," said Ferrer, 30, currently Spanish number one in the absence of injured Rafael Nadal.
Ferrer had arrived in Gijon straight from the US Open where he lost to Novak Djokovic in the semi-finals.
One of the world's finest clay-court players, along with world number 12 Almagro, Ferrer stamped out Querrey's resistance in their fiercely-fought fourth set, defending several break points in a series of dazzling rallies.
After an even start to the second match, Almagro struggled to tame Isner in the fourth set, letting slip six break points as the American giant with his feared serve blasted five aces past the Spaniard.
But the six-foot, nine-inch (206 centimetre) American's exhaustion finally showed in the deciding set, when he missed three crucial volleys as the Spaniard closed in for the kill.
"That was really disappointing because I did such a good job the whole fourth and fifth set of just hanging in there and I just kind of gave it away at the end," Isner said.
"I just tried to keep my head," said Almagro, who let slip three match points in the final game before Isner's errors handed him the match.
"I think John served really well. But I am happy. We've got two points. We've nearly won three."
The United States -- the most successful team overall in Davis Cup history with 32 victories -- admitted they were not favourites when they came to northern Spain for the tie.
But under the captaincy of former Grand Slam-winner Jim Courier, they have chalked up back-to-back away wins in Switzerland (5-0), where Isner shocked Roger Federer, and France (3-2), where he defeated Jo-Wilfried Tsonga.
Spain have dominated the Davis Cup over the past decade, winning it five times, and are surfing a wave of 23 consecutive home victories.
The pressure was on the Bryan brothers - the world's top-ranked doubles pair - to keep their hopes alive until the reverse singles fixtures on Sunday.
"Tomorrow's going to be a big a battle as well," said Courier. "Bob and Mike are extremely confident and prepared and I believe the Spanish team feel the same."
In Buenos Aires, Argentina, who have yet to win the tournament and were defeated by Spain in the 2008 and 2011 finals, opened a 1-0 lead in the other semi-final when Juan Martin del Potro beat Radek Stepanek of the Czech Republic 6-4, 6-4, 6-2.
Juan Monaco was due to meet US Open semi-finalist Tomas Berdych in the second singles rubber later on Friday.