American Varvara Lepchenko won on her Fed Cup debut to put the United States level at 1-1 against Italy on Saturday, after Sara Errani had beaten Jamie Hampton.
The 21st-ranked Lepchenko beat 16th-ranked Vinci 2-6, 6-4, 7-5 with the Italian appearing to struggle with cramp in a dramatic final set which had seven breaks of serve.
Vinci twice had treatment on court as she fought back from 5-1 down in the third to go 5-5. Lepchenko immediately broke back and served the match out.
Seventh-ranked Errani took just over an hour to win 6-2, 6-1 over Hampton, ranked 57 places below her Italian opponent.
Italy beat the U.S. in back-to-back Fed Cup finals in 2009 and `10.