Matteo Arnaldi clung on to beat Alexei Popyrin 7-5, 2-6, 6-4 and put Italy 1-0 up on Australia in the Davis Cup final on Sunday.
World number four Jannik Sinner, who defeated Novak Djokovic in singles and doubles on Saturday, can win Italy the trophy for the second time in their history if he beats Alex de Minaur in the second singles rubber.
"I think now I won one of the most important matches in my life, I don't know what to say right now," said an emotional Arnaldi.
Australia captain Lleyton Hewitt opted to maintain Popyrin in the first singles rubber, while Italy's Filippo Volandri returned to Arnaldi from Lorenzo Musetti, despite his last eight defeat in Italy's 2-1 win over the Netherlands.
Popyrin, whose nerves were jangling in the semi-final singles first set against Finland, started his first service game with a double fault after Arnaldi held to love.
Arnaldi brought up three break points the next time around with a fizzing forehand and took the third of them when Popyrin went long, for a 3-1 lead.
However world number 40 Popyrin reacted immediately by breaking back and holding, both to love, showing he would not be overawed by the occasion.
Arnaldi earned three set points but the Australian rescued them and completed a tough hold for 5-5 with two strong serves.
Popyrin wasted two break points as Arnaldi held for 6-5 and then pushed a return into the net to hand the Italian a tense first set.
The Australian was far stronger in the second set against Finland and it proved the case again, as he raced into a double break against Arnaldi, saving a break point as he held for 4-0.
Arnaldi finally got on the board in the fifth game but Popyrin -- who produced six aces in the second set to the Italian's zero -- served it out to force a decisive third set.
The erratic Arnaldi saved break points in his first, second and fourth service games without putting pressure on Popyrin's serve until earning a break point which the 24-year-old saved, holding for 4-4.
Popyrin was on top but could not make it count to get the breakthrough, with Arnaldi saving yet another break point on his way to a 5-4 lead.
Despite being outplayed for the best part of the third set Arnaldi converted his first set point to put Italy ahead in the tie with a powerful forehand.
Italy won the competition in 1976, while 28-time winners Australia last lifted the iconic cup in 2003.