Zlatan Ibrahimovic and Antonio Nocerino put the Rossoneri on the road to victory in the first half with Massimo Ambrosini scoring the third of a one-sided game in the second half.
The win lifts Massimiliano Allegri's men up to within a point of Juve, with the top two now having opened up a five-point gap over third-placed Udinese.
Cagliari remain in 13th. They host Roma in midweek while Milan travel to fourth-placed Lazio, who they beat in the Coppa Italia last week.
Milan did make light work of Cagliari, although it took them over half an hour to get ahead.
Ibrahimovic had sent one free-kick just inches wide of Michele Agazzi's post, but his second effort in the 32nd minute was unstoppable.
He curled the ball in from 25 yards with the ball just grazing the inside of the left-hand post on its way in.
Ibrahimovic then turned provider for Nocerino as he cushioned the ball down for his team mate with his chest, and the Milan midfielder did the rest with a powerful low shot into the bottom corner from the edge of the penalty area.
Nocerino, Stephan El Shaarawy and Urby Emanuelson all had chances to make it three as Milan continued to dominate the game in the second half.
The third goal finally arrived in the 75th minute with substitute Ambrosini using the outside of his right-foot to curl the ball into the bottom left-hand corner of Agazzi's goal.
Mark van Bommel went close to making it four, but three goals were enough for the Rossoneri to reduce the arrears on Juve to just a point again.