Defending champion Spain staked its claim to a place in another Davis Cup final by taking a 2-0 lead over the United States on Friday.
David Ferrer put the hosts ahead in the best-of-five series in Gijon with a 4-6, 6-2, 6-2, 6-4 win over Sam Querrey. Nicolas Almagro followed up by defeating John Isner 6-4, 4-6, 6-4, 3-6, 7-5 despite a spirited performance from the American.
The other semifinal remains finely balanced with Argentina and the Czech Republic locked 1-1 after the opening singles in Buenos Aires.
An injured and emotional Juan Martin del Potro beat Radek Stepanek 6-4, 6-4, 6-2, but teammate Juan Monaco lost 6-1, 4-6, 1-6, 6-4, 6-4 to Tomas Berdych.
The action continues with Saturday's doubles.
In Gijon, Ferrer and Almagro improved to 23-1 on clay in Davis Cup action.
Almagro overcame 25 aces from Isner, who saved three match points before hitting a forehand long to leave the defending champions one point away from their fourth final in five years.
The U.S. has only overturned an 0-2 deficit once in 38 ties - in 1934 against Australia. Since the start of World Group play, Spain is 37-0 after winning both the opening singles.
''After the effort the Americans showed today, we know that final point won't be easy,'' Spain captain Alex Corretja said. ''They've shown they've come here to give everything.''
The U.S. has to win Saturday's doubles to stay alive, and will feel confident about their chance with American brothers Mike and Bob Bryan facing Marcel Granollers and Marc Lopez. The Bryan twins are 4-0 when the U.S. is facing a 2-0 deficit, and are 5-0 against Spain.
''Nothing's impossible,'' U.S. captain Jim Courier said. ''There's no clock in tennis and it always comes down to who wins the last point.''
Del Potro, who was told by doctors not to play with the inflamed left wrist, broke down crying afterward as he addressed cheering fans at the outdoor clay-court venue.
Stepanek suggested afterward that Del Potro may have exaggerated the injury - a bit of gamesmanship - to gain Argentina an advantage.
''In truth, it wasn't easy to play,'' Del Potro said, with the crowd breaking into chants of ''Ole, Ole, Ole'' to interrupt him.
''You can see how I suffered playing. I did it for all of you. Playing here means so much for you, for the country, for Argentine tennis - for everyone and me too. I want to thank you for the love and support you have always shown me.''
Stepanek tried to work to Del Potro's backhand - where the Argentine uses his left hand on the two-hand shot. Del Potro wound up with only three winners off his backhand compared to 11 for the Czech, an indication he was playing at a disadvantage.
''There is always some pain,'' Del Potro told the crowd, which included football great Diego Maradona. ''We all have some pain - some more than others. The important thing is to try to play and do your best.''
Argentina is trying to reach its fifth Davis Cup final. It has lost all four previous finals - a record - including a year ago against Spain.
Stepanek, who complained about the crowd noise at Parque Roca, suggested Del Potro was exaggerating the injury. Speaking in Czech, he said Del Potro looked ''absolutley healthy.'' He said Del Porto's tears at the end seemed ''blown out of proportion.''
Told about Stepanek's comments, Del Potro replied: ''I wish I were perfect. I'm surprised to hear what he said, because it's not what he said to me.''
Monaco led 4-2 in the fourth set and seemed to be en route to victory. But he promptly slumped to yet another defeat by Berdych, who reached the U.S. Open semifinals.
The Argentine pair of Carlos Berlocq and Eduardo Schwank are scheduled to face Ivo Minar and Lukas Rosol in doubles on Saturday.
