Andy Murray will take Great Britain to a first Davis Cup semi-final in 33 years if he beats Italy's Fabio Fognini in Sunday's first match in Naples.
With Britain 1-0 down overnight, Murray began Saturday with a 6-4 7-5 6-3 victory over Andreas Seppi before he and Colin Fleming held off Fognini and Simone Bolelli to win the doubles.
Murray and Fleming survived a fightback to triumph 6-4 6-2 3-6 7-5.
British number one Murray will play Fognini at 10:30 BST on Sunday.
The pair have met twice before, winning one match apiece.
Should Murray, 26, repeat his victory in their most recent encounter - on clay at the Monte Carlo Masters in 2009 - Great Britain will reach the last four of the Davis Cup for the first time since they lost 5-0 to Argentina at the same stage in 1981.
Fognini has been in impressive form this season, winning 19 of 25 matches on tour, but his fitful showing in the doubles will give Murray confidence that he can win the tie for Great Britain without team-mate James Ward having to fulfil the final singles match against Seppi.
"It should be a tough match," said Murray.
"Fabio has played really well this year, especially on clay, but hopefully I can play a good match and finish the tie."
With the surface at the back of the court breaking up after heavy rain on Friday and world number 13 Fognini misfiring on serve and with his groundstrokes, the Italians were two sets down after an hour and 10 minutes.
The momentum of the match shifted after the hosts saved four break points in the third game of the third set and converted one of their own in the next.
That was enough to take the set and an unlikely victory seemed possible with the home crowd buoyant, Bolelli in a rich vein of form and the Italians serving for the fourth set.
But Murray and Fleming broke twice in succession as the erratic Fognini lost control of his serve.
"Colin came up with some good returns and I felt like we deserved to win," Murray told BBC Sport.
"Bolelli played an excellent match; he made it really tough for us and was hitting the ball huge from the back of the court."
Fleming added: "We'll find out at the end of the tie if this has been a crucial win, but it's given us the momentum going into Sunday and we couldn't be happier about that."
There was no such drama earlier in the day as Murray, resuming at 6-4 5-5 against Seppi, wrapped up victory in a further 75 minutes.
Speaking after that match, Murray criticised the condition of the court.
"It is dangerous," he said. "That back corner is not good enough. If this was on the [ATP] Tour they would not be using this court.
"That is something we will talk about after the tie because the last thing you want is for people to be injured."
The winners of the tie will go on to face Switzerland or Kazakhstan in the semi-finals, with Kazakhstan heading into Sunday 2-1 ahead after Andrey Golubev and Aleksandr Nedovyesov stunned Stanislas Wawrinka and Roger Federer 6-4 7-6 (7-5) 4-6 7-6 (8-6) in Saturday's doubles.