Argentina reached the Davis Cup final for the second time as victory in the doubles gave them an unassailable 3-0 lead over Australia in Buenos Aires on Saturday.
World number four David Nalbandian and Agustin Calleri beat Paul Hanley and Wayne Arthurs 6-4, 6-4, 7-5 to put the Argentines, losing finalists in 1981, into December's final before Sunday's reverse singles.
Russia were 2-1 up in the other semi-final in Moscow after twins Bob and Mike Bryan beat Mikhail Youzhny and Dmitry Tursunov 6-3, 6-4, 6-2.
Nalbandian had given Argentina their first point by beating Mark Philippoussis in the opening singles on Friday and Jose Acasuso finished off a see-saw five-set win over Lleyton Hewitt earlier on Saturday.
The second rubber had been suspended due to rain and fading light on Friday evening with Acasuso 4-0 up in the fifth set. He completed a 1-6, 6-4, 4-6, 6-2, 6-1 victory.
"Argentina has had a strong Davis Cup team for a long time but a lot of things have to work out for you to get to a Davis Cup final," winning captain Alberto Mancini said.
Australia's captain John Fitzgerald added: "The court was pretty slow and tough for us. It's difficult to come here and win in these conditions because Argentina have a world class team."
In Moscow, the Bryan brothers kept the US in the tie after Andy Roddick had lost to Marat Safin and James Blake had been beaten by Youzhny in Friday's singles.
"We had Andy and James coming up to us, saying 'Get us a chance, just give us another shot'," Mike Bryan said.
In Sunday's reverse singles, Roddick faces Youzhny before Blake takes on Safin.
Two of the eight playoffs were settled after only two days.
Austria and Czech Republic secured their world group status by taking unassailable 3-0 leads over Mexico at home in Portschach and Netherlands away in Leiden respectively.
Spain went 2-1 up against Italy in Santander with Rafael Nadal and Fernando Verdasco prevailing over Daniele Bracciali and Giorgio Galimberti 6-2, 3-6, 6-3, 7-6.
Switzerland also lead 2-1 after Roger Federer and Yves Allegro beat Serbia's Ilia Bozoljac and Nenad Zimonjic 7-6, 6-4, 6-4 in the doubles in Geneva.
"I think that's one of my best doubles matches ever in Davis Cup," world number one Federer said. "I was returning really well and playing very consistently from beginning to end."
In Duesseldorf, Michael Kohlmann and Alexander Waske gave Germany a 2-1 lead over Thailand with a 6-1, 6-2, 6-0 win over twins Sanchai and Sonchat Ratiwatana.
Belgium lead Slovakia, last year's losing finalists, 2-1 in Bratislava. Oliver Rochus and Kristof Vliegen beat Dominik Hrbaty and Michal Mertinak 6-2, 3-6, 6-3, 0-6, 7-5.
In the Brazilian city of Belo Horizonte, the playoff between Brazil and Sweden only got under way on Saturday.
Flavio Saretta recovered from 2-1 down to beat Andreas Vinciguerra 6-4, 1-6, 3-6, 6-2, 7-5 in the opening singles which lasted four hours and four minutes to give the home team a 1-0 lead.
The doubles in Romania's playoff with South Korea in Bucharest, which stands at 1-1, was postponed until Sunday due to heavy rain.