JOIN US
Flavia Pennetta charged past Melanie Oudin 7-5, 6-2 in the third singles rubber to give an unassailable 3-0 lead to the hosts, who were helped by Serena and Venus Williams again opting not to compete for the US.
Italy, who first won the trophy in 2006 and overcame defending champions Russia in this year's semifinals, had never beaten the Americans in nine previous Fed Cup ties.
"It's incredible, the girls have rewritten the history of Italian tennis," captain Corrado Barazzutti told reporters at the courtside before being showered with champagne.
Pennetta, the world number 11, put Italy 1-0 up on Saturday when she comfortably beat Alexa Glatch before a confident Francesca Schiavone also defeated Oudin.
The Americans, who have racked up a record 17 Fed Cup titles but have not lifted the trophy since 2000, continually struggled and failed to win a set.
Oudin, 18, gave Pennetta a great early boost by netting a simple shot and surrendering her serve in the first game.
Pennetta consistently dominated but suffered a wobble when Oudin broke back at 5-5 on the outdoor clay court. The American then double-faulted to lose serve in the next game and hand the advantage back to the Italian, who quickly sealed the set under overcast skies.
A partisan crowd in southern Italy and some slow ball girls increasingly irritated Oudin, the top-ranked US player at 49.
The fourth singles match between Schiavone and Glatch was scrapped with Italy already having triumphed, leaving Sara Errani and Roberta Vinci to entertain the fans with victory over Vania King and Liezel Huber in the doubles. They won 4-6, 6-3, 11-9 in a super tie-break instead of a third set.