Milan stunned the reigning European champions with a 1-0 victory in Miami, as Urby Emanuelson sent Chelsea tumbling.
The Rossoneri may have released many of their biggest names this summer, but are impressive in pre-season with wins over Schalke 04 and now Chelsea.
Robinho did not take part in the Miami encounter because he was turned back at Frankfurt Airport due to a passport problem. Stephen El Shaarawy therefore took the centre-forward role supported by Kevin-Prince Boateng and Emanuelson.
Milan threatened in the first half with Emanuelson and El Shaarawy failing to find the net, while John Terry slipped at the crucial moment to send a volley over. A great team move saw Massimo Ambrosini and Boateng combine to send Emanuelson clear only for him to blast off target, but the goal came after the hour mark.
Emanuelson burst through and drew the defenders, rolling across to an unmarked El Shaarawy, but his shot was deflected off Petr Cech for the Dutchman to pounce on the rebound. Milan's passing game had torn the Chelsea defence to shreds.
Daniele Bonera shepherded Fernando Torres to the by-line late on and Riccardo Montolivo almost stunned Cech from the half-way line when the goalkeeper lost his footing.
Chelsea 0-1 Milan
Scorers: Emanuelson 68 (M)
Chelsea:Cech; Ivanovic (Hutchinson 77), Luz, Terry (Cahill 60), Cole (Ferreira 60); Ramirez (Malouda 77), Obi Mikel, Lampard (Essien 77), Hazard; Meireles (Marin 46), Lukaku (Torres 60)
Milan:Amelia; Antonini (Abate 63), Bonera, Yepes (Acerbi 63), Mesbah; Traorè (Constant 80), Ambrosini (Montolivo 63), Flamini (Nocerino 63); Boateng (Valoti 74), Emanuelson (Ganz 85); El Shaarawy