AC Milan fell to a 2-1 defeat at Parma on Saturday as the seven-time European champions continued their slow start to life in Serie A under new coach Paulo Fonseca.
Matteo Cancellieri pushed home the decisive goal 13 minutes before the end of an entertaining encounter at the Stadio Ennio Tardini in which Parma defied their newly-promoted status.
The 22-year-old winger perfectly met Pontus Almqvist's low cross to score his first goal since being loaned to Parma by Lazio, who lost 2-1 at Udinese.
Milan have collected one point from their first two league matches under Portuguese Fonseca, whose team looked set to go on to take the win when in the 66th minute Christian Pulisic levelled Dennis Man's early close-range finish.
However, Parma were dangerous every time they went on the counter-attack and could have been out of sight by halftime had their finishing not been so wayward.
Milan didn't really wake up until after the half-hour mark when they tested Zion Suzuki three times in the space of two minutes, but it was still the hosts who were the more dangerous.
Simon Sohm dragged wide a great chance to double Parma's lead four minutes before the break after more excellent work from Man, this time bursting down the right and cutting in before laying off for his Swiss teammate.
And Valentin Mihaila somehow managed not to score when set clean through on goal by Ange-Yoan Bonny, dawdling on the ball and allowing Fikayo Tomori to close a yawning gap that had been left by Milan's defence.
Milan were a different team after the break and could have been level twice in the first three minutes of the second half as Tijjani Reijnders saw his deflected drive thud onto the crossbar and Suzuki did well to keep out Pulisic's low effort.
Man fell to the turf in frustration in the 62nd minute when yet another Parma counter-attack ended with his delicate curling strike wafting just wide, and moments later Pulisic had Milan level.
Rafael Leao jinked and skipped down the left before exchanging passes with Theo Hernandez and rolling in USA star Pulisic for a simple finish.
Milan pushed but it was another lightning Parma break which led to Cancellieri scoring the winner and lapping up the adulation of the joyous home crowd.
Later, champions Inter Milan make their San Siro debut for the campaign against Lecce without injured captain and star striker Lautaro Martinez, while Monza host Genoa.
Mehdi Taremi will make his first start for Simone Inzaghi's team since signing as a free agent last month, after being released by Porto.