Matteo Berrettini put Italy close to a third consecutive Davis Cup title after beating Pablo Carreno Busta 6-3, 6-4 in Sunday's first singles match.
Berrettini saw off Carreno Busta in one hour and 19 minutes in front of delighted fans in Bologna to give the reigning champions a 1-0 lead in the best-of-three tie.
Flavio Cobolli can make it three in a row for Italy by beating Jaume Munar later on Sunday.
If Munar manages to level the tie for Spain – missing world No 1 Carlos Alcaraz to injury – Simone Bolelli and Andrea Vavassori for Italy will take on Marcel Granollers and Pedro Martinez in a doubles match.
"It's hard to speak because I'm very happy and emotional, but we need to keep our feet on the ground because we have Flavio next," said Berrettini on court.
"I was a bit tense this morning but I told myself I needed to make sure I felt good on the court."
Berrettini was key to Italy retaining the Davis Cup last year and is his country's most highest profile player after Jannik Sinner and Lorenzo Musetti both chose not to take part in the Azzurri's title defence on home soil.
Their absences, and Alcaraz dropping out for Spain due to injury, has left this year's finals lacking stardust.
But earlier on Sunday the head of the International Tennis Federation insisted that top players were not snubbing the competition.
"There's this false feeling out there that top players don't represent their nation. That's not true," David Haggerty told reporters ahead of Sunday's final.
"Some of those top players that played in the qualifier round or the second qualifier round didn't make it to the finals. And so we had many top players that have played."
American Taylor Fritz, Australian Alex de Minaur, Dane Holger Rune and Norwegian Casper Ruud – all in the top 20 of the men's rankings – featured in the early rounds of the competition without managing to reach the finals with their respective nations.