Josip Ilicic scored twice as Atalanta outclassed a sorry Milan with a 5-0 rout in Bergamo on Sunday.
The hosts were rewarded for a dominant opening with a wonderful solo goal from Alejandro Gomez and ex-Rossoneri midfielder Mario Pasalic doubled the lead shortly after the hour.
Ilicic drilled home in the 63rd minute and soon had a second with an exquisite effort as Atalanta - who completed the thrashing through substitute Luis Muriel - were rewarded for a display full of enterprise and invention with a result that sees them head into Serie A's mid-season break in fifth.
Milan, who were unbeaten in four prior to the game, and coach Stefano Pioli will need to do some soul searching over the next fortnight, though, after a woeful away performance.
Ilicic had already tested Gianluigi Donnarumma by the time Gomez opened the scoring with a sublime piece of skill after 10 minutes.
The forward nutmegged Andrea Conti on the left wing and drove inside before hammering high into the far corner.
Pasalic also rattled the crossbar and a ramshackle Milan, whose best first-half effort was a long-ranger from Ricardo Rodriguez, were fortunate Mateo Musacchio's elbow on Gomez only drew a yellow card.
Ruslan Malinovskiy placed a 20-yard effort just past the right post but a quickfire double had Atalanta in control.
Pasalic touched in Robin Gosens' strike from the left of the area, with Conti again beaten easily, before Ilicic turned Davide Calabria and rifled past a helpless Donnarumma less than two minutes later.
The best was still to come, though, with Ilicic jinking and weaving before cutting onto his left from 20 yards and bending a fine strike into the top-left corner.
Muriel, who replaced the brilliant Ilicic, made it five in the 83rd minute after racing onto a long ball and rounding the onrushing Donnarumma to tap into the open goal.
What does it mean? Woe in Bergamo for Milan
There were signs Milan were on the road to recovery after taking eight points from the previous four Serie A matches, but this was as hapless a showing the Rossoneri have produced during an underwhelming season. Isolated in attack, light in midfield and disorganised at the back, Pioli has much to ponder.
Ilicic the guide for fluent Atalanta
By contrast there was much to admire about Atalanta, whose front three caused Milan all manner of trouble. At the heart of it was Ilicic, who had forced Donnarumma into action twice before his goals. Gomez also impressed and had Conti on toast for his wonderful opener, while Pasalic – who did not celebrate against his former club – was always a creative outlet.
Conti emblematic of Milan's misery
Not many in a Milan shirt came out with much credit here, but Conti had a particularly torrid time and was culpable for Atalanta's opening two goals.
Atalanta resume after the mid-season break with a home fixture against Parma on January 6, the same day Milan welcome Sampdoria.