Italian Cristiana Girelli, 30, scored the only goal of the match on a penalty after just 12 minutes.
The first half was even in terms of play, but in the second Milan took over completely.
They had many chances to equalize when, among others, Valentina Bergamaschi, team captain Valentina Giacinti and Deborah Salvatori Rinaldi had positions.
But the Juve defense, led by Sembrant, weathered the storm and took three new points.
Lina Hurtig came on, Girelli had to leave the fray.
Juventus, who have won the league three years in a row, lead Serie A with four straight victories.
The loss was Milan's first this season.