Spain pulled level with Argentina in the Davis Cup final on Friday when Feliciano Lopez stunned an ailing Juan Martin del Potro in four sets.
Lopez, 31st in the world rankings, won 4-6, 7-6, 7-6, 6-3 in three hours 19 minutes to wipe out David Nalbandian's straight sets win over David Ferrer in the opening rubber.
Del Potro, already troubled by a toe injury, appeared to pull a muscle in his right leg in the sixth game of the fourth set and needed about 10 minutes of treatment.
"Tennis matches are like that," said Lopez, who was chosen by captain Emilio Sanchez Vicario ahead of the higher-ranked Fernando Verdasco.
"I was a bit nervous at the start, I got over it in the second set and began to believe in myself more. It was a victory over myself."
"To beat a top ten player this way, in a Davis Cup final away from home, is the happiest moment in my career."
"There were moments in the second and third sets where I felt I could not have played any better."
Del Potro said it was too early to say whether his injury would keep him out of Sunday's reverse singles.
"He played really well, above himself," said the 20-year-old of his opponent.
"I'm a bit surprised by the standard he played. He didn't commit double faults, his second serve was almost as good as his first and I couldn't find a way past him."
Del Potro, ranked ninth, swept through the first set in 38 minutes and appeared set to carry on where Nalbandian had left off.
Lopez had other ideas and hit back to win the next two sets in tiebreaks after all games went with serve.
He reeled off the first tiebreak 7-2 and, in the second, came back from 4-2 behind to win four points in a row and clinch the breaker 7-4 with an ace.
With the crowd at the Polideportivo Malvinas arena increasingly quiet, Lopez continued his dominance by breaking in the fourth game of the fourth set, helped by two Del Potro double faults, to take control.
Already looking fatigued after a long season that has seen him leap from obscurity into the top 10, Del Potro managed to break back immediately but then suffered his injury in the next game.
He soldiered on but Lopez wrapped up the match comfortably.
Argentina, unbeaten at home in 10 years, went into the final as firm favourites to win the competition for the first time against opponents missing injured world number one Rafael Nadal.
The first match went according to the script as Nalbandian thumped Ferrer 6-3, 6-2, 6-3 in one hour 59 minutes to give the hosts the perfect start.
"I played well from start to finish, I was always in control of the situation and the public was incredible," said Nalbandian. Ferrer was dejected.
"I felt inferior," he said. "David was far superior and there's nothing more to say."
Sanchez supported his number one player. "He was up against one of the best in the world on this surface and I don't think he was so bad."