The Islanders, seeking back-to-back league wins for the first time since March, started in a confident manner and saw Nicolas Viola hook an acrobatic effort over the bar early on. At the other end, Rafael Leão sent a swinging effort from outside the area straight at the goalkeeper, while Theo Hernandez had a strike deflected narrowly wide as the hosts started to turn the screw.
Christian Pulisic was the next to have a go, although his low drive from 25 yards resulted in a reasonably straightforward save for Elia Caprile, who also thwarted Tijjani Reijnders.
It looked like only a matter of time before the deadlock was broken, but the visitors were giving as much as they could to, with Mattia Felici forcing the stop of the half from Mike Maignan, who sprung high to his right to tip a whipped effort that was heading for the top corner around the post.
Milan still had the bulk of the chances though and were inches away from going 1-0 up two minutes into the second half when Pulisic rattled the bar with a fierce effort from distance.
Alvaro Morata then hooked into the side netting from a near impossible angle, but the evergreen striker could make no mistake with his next attempt, sliding into an empty net from inside the six-yard box after Pulisic’s volley had deflected his way off the post.
A resilient Cagliari hit back immediately, equalising within four minutes through a low, angled Nadir Zortea strike that Maignan should have saved, but it slipped under his flailing body.
The Rossoneri were undeterred though, as Caprile made a pair of fine stops from Youssouf Fofana and Pulisic, before Hernandez, too, was denied.
Leao then looked destined to make it 2-1 when he beat the offside trap to burst onto a through ball, only for the goalkeeper to make another sprawling save.
In the end, Milan’s pressure was not rewarded, with Caprile making another terrific stop deep into injury time from a fizzing Hernández free kick.
It means the hosts have now won just one of their last five league outings, while Davide Nicola’s side, who had picked up one victory in the previous 39 head-to-heads this century, remain in the relegation zone, despite registering a valuable point.