Italian number one Flavia Pennetta beat American teenager Melanie Oudin 7-5 6-2 as Italy won the Fed Cup 3-0 in Reggio Calabria.
The hosts won the opening two singles on the clay court on Saturday, with Pennetta and Francesca Shiavone beating Alexa Glatch and Oudin respectively.
The 18-year-old Oudin, at number 49 the Americans' highest-ranked player, lost her serve in the first game.
World number 11 Pennetta consistently dominated but allowed Oudin to break back for 5-5.
The American then double faulted to lose her serve in the next game and hand the advantage back to the Italian, who quickly sealed the set.
Oudin fell apart in the second set and was broken three times, with Pennetta dropping her own service just once more on the way to victory.
"It's incredible, the girls have rewritten the history of Italian tennis," said Italy team captain Corrado Barazzutti.
The Americans - missing their top-ranked players Serena and Venus Williams - failed to win a set on their way to a first defeat in 10 Fed Cup ties against Italy.
It is Italy's second Fed Cup title in the last three years.
The United States did manage to win a set in the 'dead' doubles rubber but were beaten nontheless, Sara Errani and Roberta Vinci beating Liezel Huber and Vania King 4-6 6-3 11-9
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