The meeting, which took place at the Renato Dall'Ara stadium, ended in a victory for the guests with a score of 4: 2.
Rafael Leau, Davide Calabria, Ismael Bennasser and Zlatan Ibrahimovic scored for Milan.
Musa Barrow and Zlatan, who sent the ball into his own net, scored for Bologna.
The hosts finished the match with nine players.
On the 20th minute, Adam Sumaoro was sent off the field, and on the 58th - Roberto Soriano.
The Milanese lead the standings with 25 points.
Bologna have 12 points and the ninth line.
Earlier, Porto beat Milan in the Champions League match.