Roberta Vinci sent Italy into the Fed Cup final for the fifth time in eight years with a 6-2 6-7 6-3 victory over Czech Republic's Lucie Safarova in Palermo on Monday.
The match was held over because of rain on Sunday.
Vinci's triumph gave Italy, winners of the trophy in 2009 and 2010, an unassailable 3-1 lead over the twice defending champions, meaning the doubles was not played.
Russia await in the final after they stormed back from 2-0 down to beat Slovakia 3-2 in Moscow on Sunday.
Italy went 2-0 up on Saturday before Petra Kvitova gave the Czechs hope on Sunday by beating Sara Errani in front of a partisan crowd at the Circolo Tennis Palermo.
Vinci, 30, had too much guile for Safarova in the first set although the Czech found her feet in the second to lead 5-3.
The Italian broke back and served for the match at 6-5 but faltered and was brushed aside in the tiebreak by an inspired Safarova.
In the decider Vinci gave up a 2-0 lead but then broke serve to lead 5-3 and even though she failed to convert her first two match points she made no mistake on the third.
"It's an incredible moment for me," said Vinci after being doused with water by her joyful team mates.
"I was nervous and a bit tired. I've played Fed Cup for a long time and it will be great to play Russia in front of these fans in the final."
Italy will have home advantage against Russia, the team they were beaten by in the 2007 final.
"Roberta was unbelievable today," said captain Corrado Barazzuti. "I was a bit worried in the third set because Roberta was 2-0 up and then it became a very difficult match."
(Reporting by Martyn Herman in London, editing by Tony Jimenez)