Russia clinched their second Davis Cup title with a thrilling 3-2 victory over Argentina in Moscow.
Safin's serving was superb against Acasuso
Marat Safin, inspired by the passionate home crowd, claimed a 6-3 3-6 6-3 7-6 (7-5) win over Jose Acasuso in the deciding singles rubber.
David Nalbandian had earlier kept Argentina's hopes alive after beating Russia's Nikolay Davydenko in the penultimate singles match.
Nalbandian won 6-2 6-2 4-6 6-4 to draw the tie level at 2-2.
Safin, the former US Open and Australian Open champion, had been drawn to play Juan Ignacio Chela in the final match, but Argentina captain Alberto Mancini replaced him with Acasuso.
It was Acasuso's first appearance in the final although he was unbeaten in his four previous Davis Cup matches this year.
The Russian, who had won only one of his previous three meetings with Acasuso, came out strongly, breaking his rival's first service game to move ahead 3-0 and he served out the first set in 30 minutes.
I was afraid I could lose the match if I failed to win the tiebreak
In the second the 24-year-old Argentine bounced back to break Safin's serve in the sixth game and level at one set all.
But boosted by his home crowd, including former Russian President Boris Yeltsin, Safin's confidence returned and he broke twice in the third set to put himself in control.
The fourth set was a tight affair that was decided by a tie-break, which Safin edged after Acasuso netted a forehand to spark wild celebrations.
"I'm happy to win in front of my home fans," Safin said after the match. "It was really hard to win as I experienced serious problems with the surface as I failed to adjust my playing to the carpet.
"I'm glad I won in four sets. I was sure Nikolay (Davydenko) would win his match but after he lost I was pretty nervous.
"I also have problems with my heel and knees. I was afraid I could lose the match if I failed to win the tiebreak."
"I'm very happy for all of us and all of our fantastic supporters," he added.
Davydenko beat Chela in Friday's opening match but Nalbandian then beat Safin to even the score.
On Saturday, Russia took a 2-1 lead when Safin and Dmitry Tursunov got the better of Nalbandian and Agustin Calleri in the doubles.