Defending champions Spain will face the Czech Republic in November's Davis Cup final after beating the United States 3-1 in Gijon.
David Ferrer beat John Isner in four sets to ensure victory after Spain had won the opening two singles matches.
The Czech Republic, defeated by Spain in the 2009 final, beat last year's runners-up Argentina 3-1.
Tomas Berdych sealed the win by beating Carlos Berlocq, who played instead of the injured Juan Martin del Potro.
Spain are hopeful that Rafa Nadal will recover from a knee injury in time to help their attempt to retain the title.
Nadal, a winner of 11 majors, has not played since his shock second-round exit against Czech Lukas Rosol at Wimbledon in June.
"I hope he gets better soon because he is really fundamental for us," said Ferrer.
World number five Ferrer, beaten by Novak Djokovic in the US Open semi-finals, got Spain off to a good start in the tie, played on clay, by beating Sam Querrey 4-6 6-2 6-2 6-4 on Friday.
Nicolas Almagro then beat Isner 6-4 4-6 6-4 3-6 7-5 to put Spain in a commanding position.
Twins Bob and Mike Bryan gave the Americans hope with their 6-3 3-6 7-5 7-5 win over Marcel Granollers and Marc Lopez in Saturday's doubles match, and Isner got off to a good start on Sunday.
He took the first set in a tie-break but 70 unforced errors to Ferrer's 32 meant the Spaniard was able to battle back and seal a 6-7 6-3 6-4 6-2 win despite the American hitting 11 more aces.
In the other semi-final in Buenos Aires, also played on clay, Del Potro beat Radek Stepanek 6-4 6-4 6-2 in Friday's opening singles match.
World number six Berdych levelled the tie with a 6-1 4-6 1-6 6-4 6-4 victory over Juan Monaco.
Berdych and Stepanek gave the Czechs the advantage by winning Saturday's doubles match, beating Berlocq and Eduardo Schwank 6-4 6-3 6-4.
Del Potro, the world number eight, had been due to face Berdych in the singles on Sunday, but had to pull out after aggravating a left wrist injury, with Berlocq going down 6-3 6-3 6-4.