Gabriel Paletta grabbed the winner as AC Milan produced a sensational fightback to win a barmy Serie A encounter 4-3 against Sassuolo at San Siro on Sunday.
The seven-time European champions had initially led through Giacomo Bonaventura's strike, but, after conceding almost immediately to Matteo Politano, their defence fell to pieces.
Sassuolo added further goals in quick succession in the second half, with Francesco Acerbi and Lorenzo Pellegrini stunning the home crowd into silence.
However, Carlos Bacca's penalty and then Manuel Locatelli's glorious effort brought Milan back level, before Paletta's header completed an incredible comeback.
The visitors had been in Europa League action on Thursday - travelling to Belgium to face Genk - and it told in the closing stages as Vincenzo Montella's men took control.
Milan started brightly when, in the ninth minute, their first shot led to the opener.
Bonaventura skipped clear of the midfield to strike at goal, but his effort deflected off the desperate lunge of former Rossoneri defender Acerbi and flew past Andrea Consigli.
However, a home defence missing the injured Alessio Romagnoli quickly granted Sassuolo a reprieve.
Ignazio Abate gifted the ball to Politano, who ran through the gaping hole in Milan's back line to coolly finish beyond the stranded Gianluigi Donnarumma.
Sassuolo then had Claud Adjapong's goal ruled out for handball, but kept pushing, with Pellegrini testing Donnarumma from the edge of the area, before the Milan goalkeeper was fortunate to escape punishment as he appeared to foul Politano when the goalscorer stole possession.
Carlos Bacca sought to muster a response to the away side's dominance, but having picked out Mattia de Sciglio on the left, he swiped wildly at the return cross and missed the target.
Bonaventura flashed wide shortly after half-time, while Consigli saved when Suso dipped inside to shoot and Juraj Kucka nodded over.
But, as in the first half, Milan's momentum soon slowed and Sassuolo again took advantage.
Acerbi met Pellegrini's deep cross to volley the visitors into the lead, and worse was to follow for Montella.
Pellegrini grabbed a goal himself just two minutes later, wonderfully dancing onto his left foot to curl into the far corner.
However, substitute M'Baye Niang then tangled with Luca Antei in the area, allowing Bacca to rifle home from the spot and drag his side back into the game.
Milan now had their tails up against the tiring Sassuolo, with Locatelli rifling into the top corner from the edge of the area to level the scores.
There were fine saves at both ends to deny Bonaventura and Politano, but the eventual winner was Paletta's in the 77th minute.
Storming onto Niang's cross, the 30-year-old nodded across Consigli into the far corner to claim the points in improbable fashion.