Inter Milan suffered another wobble in their bid to reclaim the Serie A title after Saturday's 1-1 draw with Atalanta, who bounced back from Champions League humiliation against Bayern Munich.
Nikola Krstovic earned a point for Atalanta by scoring in the 82nd minute at the San Siro, cancelling out Pio Esposito's angled drive after 26 minutes for the hosts, who had looked to be extending their league lead to 10 points.
But Inter coach Cristian Chivu and his players were livid at Krstovic's goal being awarded after what they saw as a push on Denzel Dumfries by Kamaldeen Sulemana, whose saved shot led to the leveller.
Chivu was sent off for his vehement protests against the officials in a heated end to what had up to that point been a humdrum affair in soaking wet Milan.
Dumfries held his head in his hands when referee Gianluca Manganiello pointed to the centre circle to give the goal, which handed AC Milan the chance to move to within five points of their local rivals.
Milan, who prevailed in their local derby with Inter last weekend, travel to Rome to take on Lazio on Sunday night and can reignite a title race which looked as good as over a week ago.
A fighting point for Atalanta came after Tuesday's humiliating 6-1 defeat to Bayern in the Champions League, a competition for which they are just about in contention to qualify this season.
Atalanta are four points behind Como and Roma, who are separated by goal difference in fourth and fifth, and face off on Sunday.
Juventus, a point behind that pair in sixth, can move into the top four with a win at Udinese in Saturday's late match.
Reigning champions Napoli trail Inter by 12 points in third place but can cut that gap against Lecce in Naples, where Antonio Conte's team are yet to lose a league fixture this season.