Williams, who accepted a wild-card invitation for the Parma tournament after losing her opening match at the Italian Open last week, dominated after dropping her serve in the opening game.
"I'm just starting to feel more comfortable. I've always felt super comfortable on the clay and this year has been a little more difficult than normal," said Williams, who served six aces. "I think it was because of the long hiatus I've had (from) the clay."
Williams is preparing for Roland Garros, which starts in two weeks. Her previous win on clay came in the first round of last year's tournament in Paris.
It was the first WTA tour match for Pigato and the 1,001st for Williams, a 23-time Grand Slam champion.
Pigato asked Williams to pose for a photo with her on court immediately after the match ended.
"It was really cool and gutsy," Williams said. "She's going to look back (in) years and be like, 'Well, this was my first match.' I wish I had done that with my first match, it would have been really cool."
Ranked No. 572, Pigato won the girls' doubles title at last year's French Open with Eleonora Alvisi.