The result leaves the famous Italian giants in 11th place in the Serie A table—30 points off Juventus in top spot, 20 points off the third, final Champions League qualifying position and nine points off bitter rivals Internazionale.
The decision had already been made to change managers in the summer, with Allegri acknowledging the recent Christmas break was the last he would spend as the Rossoneri coach, but some especially poor showings have forced Silvio Berlusconi and Adriano Galliani's hand.
In truth, the sacking was a long time coming.
It's difficult, perhaps impossible, to place the blame of Milan's alarming slide into mediocrity solely on Allegri's shoulders. Injuries, poor form, player mistakes and suspect acquisitions have all played their part too.
The crowd and fanbase have been (largely) anti-Allegri since last summer, so the former Cagliari tactician was always set to fight an uphill battle. Their opening-day loss to Hellas Verona—who, despite turning out to be a surprise package, were a newly promoted outfit at the time—compounded the fears.
Stephan El Shaarawy has made a total of two starts in an injury-plagued season, Giampaolo Pazzini has missed six months with a severe ailment, Keisuke Honda and Adil Rami have arrived too late and the squad is packed with average depth players.
We have seen some truly great Rossoneri sides in the past and perhaps this does't come close to the glories of old, but with Mario Balotelli, Kaka, Ignazio Abate, Mattia De Sciglio, Nigel de Jong, Riccardo Montolivo and more, Allegri should have been doing far, far better.
Perhaps they don't boast the depth Juventus or Napoli do, but man-for-man as a best XI they rival most top clubs in football.
At this moment in time the Rossoneri looks a bit of a dumpster fire, but once a few flames are doused it becomes an incredibly attractive, rare job to walk into.
For the rest of the season, the new manager will enjoy a pressure-free campaign to work his magic; if he achieves success he did it with a "broken" squad, if not it was because of Allegri's shortcomings haunting the side.
They will inherit a world-class forward, a prime playmaker coming back to his best, an improving defence and a solid, if unspectacular, defensive midfield. The pieces are largely in place no matter how many times people criticise the quality of the XI, and where Allegri has failed, the new man will likely succeed.
An adequate cross-sport comparison looms in the form of the Detroit Lions, who have all the quality and key pieces in place but simply require a new authoritative figure to help them iron out basic errors.
Milan can reload and come back stronger despite the daunting points gap between themselves and the upper Serie A echelons, and it could well be a fun ride until season's end.
Clarence Seedorf, Filippo Inzaghi and Mauro Tassotti are the names in the hat at this early stage; while this sinking Rossoneri ship won't make the Champions League this season, it represents the perfect chance for an inexperienced or young coach to come in, cut their teeth and prosper.