AC Milan wasted an opportunity to extend their six-game unbeaten run and go top of Serie A after a 3-0 defeat at Genoa.
A win would have moved the Rossoneri ahead of Juventus, who play Sampdoria on Wednesday, but Vincenzo Montella's men could not reproduce the performance that led to victory over the Italian champions at the weekend.
Nikola Ninkovic's first-half header, a Juraj Kucka own-goal and smart finish by Leonardo Pavoletti within the last 10 minutes secured victory for Genoa in a bad-tempered game at Stadio Luigi Ferraris, with Gabriel Paletta dismissed for Milan after a wild two-footed challenge.
Milan rarely threatened against an organised Genoa side that resolutely defended their early lead, and Montella will hope the defeat is a temporary setback for his young side before hosting Pescara on Sunday.
Their job was made much harder by Paletta's dismissal early in the second period, but the win is much-needed tonic for Genoa who had won just one of their past six outings.
Lax Milan defending allowed the hosts to take an 11th-minute lead when no-one tracked the run of Ninkovic, allowing the winger to meet a pinpoint Tomas Rincon cross and steer his header beyond Gianluigi Donnarumma for his first goal for the club.
During the first half, the visitors struggled to find the form that has propelled them up the Serie A standings, thwarted by Genoa's dogged persistence in protecting their early lead.
Their often five-man defence crowded Milan's attacking players whenever they found possession in dangerous areas and off-target shots from distance by Alessio Romagnoli and M'Baye Niang represented Milan's only sights of goal during the opening period.
Milan started the second half brightly, and tested Genoa keeper Mattia Perin twice within five minutes of the restart.
First Perin diverted Giacomo Bonaventura's drive wide of the post, then from the resulting corner he was alert enough to get to the ball ahead of Kucka as it fell kindly to the Milan midfielder in the six-yard box from a clever touch by Carlos Bacca.
There were constant flare-ups between the two sets of players throughout the game, and the visitors' task got much harder in the 56th minute when Paletta was given a straight red for a two-footed lunge on Luca Rigoni.
Buoyed by their numerical advantage, Genoa began to press for their second and Rincon went close when he curled an effort just wide of Donnarumma's post from the edge of the area.
Perin held fierce drives from Kucka and substitute Suso from outside the box as Milan tried desperately to salvage an equaliser.
But it was Genoa who did grab their second in the 79th minute when Kucka turned the ball into his own net following a well-directed low cross from substitute Darko Lazovic.
Salt was then really rubbed into Milan wounds with just five minutes to play, when fellow Genoa substitute Pavoletti hared onto a through ball, cleverly cut inside onto his right foot and steered the ball past Donnarumma to seal an impressive victory for the hosts.