Without world number one Rafael Nadal, resting his knees after his French Open and Wimbledon triumphs, Spain slipped behind when Gael Monfils (pictured) beat David Ferrer 7-6 6-2 4-6 5-7 6-4 before Michael Llodra saw off Fernando Verdasco 6-7 6-4 6-3 7-6.
Spain are going for a hat-trick of titles but will have to win Saturday's doubles and both reverse singles on Sunday to stay in the competition.
Russia and Argentina, the winners of whom will face either France or Spain in the semi-finals, were locked at 1-1 after the opening singles in Moscow.
David Nalbandian, whose ranking has plummeted into the 150s after injury problems, gave Argentina a superb start with a 6-4 7-6 7-6 defeat over Nikolay Davydenko before Mikhail Youzhny outclassed Leonardo Mayer 6-3 6-1 6-4 in two hours six minutes.
"We both didn't play our best but I won and it was the most important thing," Nalbandian, who has been troubled with hip and leg injuries, said.
"We made a lot of mistakes today but physically I felt fine. If the match went into a fourth or even a fifth set I think I would have played with the same intensity."
Davydenko, who lost both tiebreaks after letting a 5-2 and 6-4 leads slip away, was left to rue missed chances.
"I don't have a lot of confidence because I didn't play a lot of matches this year," said the world number six, who is also on a came back trail after missing nearly three months with a wrist injury.
In the bottom half of the draw the Czech Republic, without their two best players in Radek Stepanek and Wimbledon runner-up Tomas Berdych, enjoyed a sensational opening day against Chile, racing into a 2-0 lead in Coquimbo.
Ivo Minar dropped just five games against Nicolas Massu before Jan Hajek thrashed Paul Capdeville 6-0 6-2 6-1.
World number two Novak Djokovic gave Serbia a solid start against regional rivals Croatia in Split, beating Ivan Ljubicic 7-6 6-4 6-1 before Marin Cilic hit back for the hosts with a comfortable victory against Viktor Troicki.
"The first set was really tough, plus it's never easy to play away from home, but I managed to convert my break chances and seize control over the match," Djokovic told reporters.
Monfils, taking on the lead role for France in the absence of Jo-Wilfried Tsonga, appeared to be cruising against Ferrer when he won the first two sets on the indoor hardcourt.
However, Ferrer launched a robust fightback and levelled the match before Monfils edged home to the delight of most of the 6,000 crowd.
Ferrer had won his previous eight matches in Davis Cup.
"I feel happy. Not relieved, just happy," Monfils, who fired down 21 aces, told reporters. "I felt strong and I really fought hard on the crucial points... and the crowd support helped me."
Verdasco was plagued by unforced errors against the attacking Llodra but did nick the first set on a tiebreak after saving two sets points.
Llodra seized control thereafter and Verdasco crumbled before staging a late rally in the fourth but the home favourite won to put France one point away from a first Davis Cup win over Spain since 1923.
Ominously for Spain, they have never recovered after losing the first two singles matches.