Marin Cilic overcame Federico Delbonis 6-3, 7-5, 3-6, 1-6, 6-2 after a titanic tussle in the opening singles rubber to give hosts Croatia a 1-0 lead over Argentina in the Davis Cup final on Friday.
Argentine Juan Martin Del Potro faces big-serving Ivo Karlovic in the day's other match at a packed Zagreb Arena, including several thousand passionate away fans led by the south American country's former World Cup winner Diego Maradona.
Roared on by an equally fervent home crowd, Cilic rained down a barrage of aces and service winners in the opening set, having broken Delbonis in the fourth game to edge ahead.
Cilic, the world number six, broke again in the 11th game of the second set and held serve to take a commanding 2-0 lead before Delbonis hauled himself back into the match.
The 41st-ranked Argentine saved three break points in the seventh game of the third set and claimed it with a searing forehand winner.
He could not miss in the fourth, racing through the set with a barrage of spectacular shots against a subdued Cilic.
The resurgent Croatian found another gear in the fifth set, however, breaking Delbonis in the second game and again in the seventh before he closed out the match in three hours and 30 minutes.
