The Italian defender gave Stefano Pioli's men an early lead in Bergamo that inspired them to pick all three points on the road
David Calabria scored AC Milan's third fastest goal in the Serie A since the 2004-05 season, after Rafael Leao and Sulley Muntari.
Calabria opened the scoring for the Rossoneri after 28 seconds into their clash against Atalanta as they later grabbed a 3-2 victory on Sunday.
Leao's six seconds strike against Sassuolo remains Milan's fastest league goal in 16 years while Muntari's 18 seconds opener against Juventus is the second-fastest.
Editors' Picks
Goals from Sandro Tonali and Leao later in the game helped the visitors overcome a late comeback at Gewiss Stadium, with Atalanta scoring two late goals in the 86th and 94th minutes.