Fernando Llorente scored twice as Juve made it 11 league wins in a row.
Mauricio Pinilla put Cagliari in front, but his day ended badly with a late red card which completed the hosts' misery.
Llorente levelled it up before half-time and Claudio Marchisio, just on as a substitute, made it 2-1 with a fine strike.
Llorente tapped in the third before the impressive Stephan Lichtsteiner made it 4-1.
Manchester United manager David Moyes was in the crowd and, after a bright start by the visitors, he saw them go behind in the 21st minute.
A corner picked out Pinilla, who scored at the far post.
Daniele Conti almost made it two as he headed narrowly over from another corner and Cagliari continued to create chances, with Pinilla bringing a save out of Gianluigi Buffon with a shot from the left-channel.
Juve equalised in the 31st minute, Lichtsteiner and Llorente linking up, as they did well all game, and the Spaniard firing his team-mate's right-wing cross into the bottom corner.
Buffon had to be alert again to keep out a close-range Daniele Dessena header with his feet, while at the other end Arturo Vidal tested Antonio Adan in the home goal.
Lichtsteiner missed a great chance when he fired over just before half-time, while Paul Pogba was also off target from much further out shortly after the break.
Juve were in their stride now and Carlos Tevez turned and shot from the edge of the area, Adan saving well.
The Argentinian worked Adan again from outside the area before Marchisio found a way past the keeper in the 73rd minute.
Introduced for Andrea Pirlo seven minutes earlier, Marchisio left fly with a shot from 30 yards which beat Adan at his near post.
Llorente added a third two minutes later, slotting home Lichtsteiner's ball across the goal.
And the roles were reversed for the fourth in the 80th minute as Lichtsteiner followed up to score after Adan had saved Llorente's shot from the edge of the area.
And things got even worse for the hosts in the 87th minute when Pinilla was shown a straight red card for dissent.