The unheralded Karol Beck and Dominik Hrbaty posted surprise wins for the hosts at the Bratislava Tennis Centre to plunge the champions into crisis.
The only surviving member of the 2004-winning side Rafael Nadal and his partner Albert Costa must win their doubles rubber on Saturday otherwise Spain will repeat their feat of 2001 when they fell at the first hurdle as champions.
Beck beat Feliciano Lopez 6-4 7-5 6-3 and Hrbaty downed Fernando Verdasco 6-3 6-4 6-7 6-3 on a lightning-quick carpet court about which the Spaniards had bitterly complained.
"Beck was better than me in every aspect of play. He didn't give me much of a chance," a battered Lopez said.
"I've never seen him play so well. He surprised me with the level at which he played."
Argentina lead the Czech Republic 2-0 in Buenos Aires after David Nalbandian beat Jiri Novak 4-6 6-2 6-3 6-4 and Guillermo Coria downed Tomas Berdych 6-3 3-6 6-0 6-3.
France and Sweden are locked at 1-1 in their tie after Thomas Johansson pulled the Swedes back into the match with a 6-4 6-4 7-6 win over Sebastien Grosjean.
Paul-Henri Mathieu earlier gave the hosts the perfect start in Strasbourg with a 6-3 6-2 6-4 win over Joachim Johansson. "I was in control of the match from the start," said Mathieu.
Grosjean, just over a thigh injury that caused him to miss the Australian Open, was unable to build on Mathieu's lead. Up against a solid opponent he simply made too many errors.
United States will lock horns with Croatia in Los Angeles later.
COMMANDING LEAD
In Sydney, a resurgent Wayne Arthurs and Lleyton Hewitt put Australia in a commanding 2-0
Oozing confidence since capturing his first career title in Arizona last weekend, Arthurs overcame Austrian number one Jurgen Melzer 7-6 6-2 6-4. Hewitt had earlier outclassed Alexander Peya 6-2 6-3 6-4.
Australia can close out the tie in Saturday's doubles, when Arthurs will team up with the nation's most successful doubles player Todd Woodbridge against Peya and Julian Knowle.
"It's a relief to be 2-0, a very handy position," Australia captain John Fitzgerald said.
Australian Open champion Marat Safin took just over two hours to cancel out Chile's early advantage in Moscow, Safin defeating Adrian Garcia 6-1 3-6 6-3 7-6 to ensure proceedings are level after day one.
Fernando Gonzalez had earlier given the visitors the perfect start, beating Mikhail Youzhny 7-6 5-7 6-3 7-6.
"I'm really, really happy for my country," said 24-year-old Gonzalez, a singles bronze medallist and doubles gold medallist at the Athens Olympics.
Safin blamed the super-quick court specially laid in Moscow to put the Chileans at a disadvantage.
"I could not find my timing and rhythm on this surface," the world number four said.
But he added: "We remain the favourites... we are expecting to lead 2-1 after tomorrow. We have to win tomorrow."
In Saturday's doubles Gonzalez and Garcia will face fresh Russian pair Igor Andreev and Nikolay Davydenko.
Romania's Andrei Pavel squeezed past Vladimir Voltchkov to haul the hosts back into contention after Belarussia had taken an early lead thanks to Max Mirnyi.
Pavel took 2-1/2 hours to edge it 6-4 7-6 7-6 after Mirnyi had beaten Victor Hanescu 7-6 6-4 3-6 6-4.
The Netherlands eased to a 2-0 lead in Switzerland thanks to victories from Sjeng Schalken and Peter Wessels.