The second-seeded Italians beat Andrea Hlavackova and Lucie Hradecka 6-4, 6-2 Sunday for their second Grand Slam championship -- and second in three months after they broke through at the French Open.
The best friends faced each other in the singles quarterfinals at Flushing Meadows, with Errani winning to become the first Italian women to reach the semis at this tournament in the Open era.
Errani was also the runner-up in singles at Roland Garros. Vinci's quarterfinal run this week was her best individual performance at a major tournament.
Unlike their singles matchup, when Errani didn't even smile after winning, both yelled and danced after Sunday's victory.
Hlavackova and Hradecka, the third-seeded Czech team, won last year's French Open.
Samantha Crawford became the second straight American to win the U.S. Open girls title, defeating Anett Kontaveit of Estonia 7-5, 6-3 in the final Sunday.
In the boys final, Filip Peliwo of Canada added the U.S. Open to his 2012 Wimbledon title with a 6-2, 2-6, 7-5 victory over Liam Broady of Britain.
Crawford received a wild card into qualifying for the women's tournament and won three matches to make the main draw in that event.
She fell in the first round there to Britain's Laura Robson, but swept through the girls draw. Last year, American Grace Min won the girls title.