The 182nd Serie A Derby della Madonnina was thrilling to the end as Stefan de Vrij (32) netted in the 93rd minute to assist Inter Milan in drawing with AC Milan and preventing a second consecutive loss to them.
It was an even contest in the first half, and both sides desired to triumph.
Federico Dimarco had scored in Mike Maignan's goal after seven minutes, but the attempt was voided because Lautaro Martinez had been out of position when he played the ball into his path.
Christian Pulisic had a shot blocked and it went out for a corner.
Nicolo Barella had a shot saved as well. Both teams were playing well, but their tight defense was making it hard to score.
Inter Milan started gaining control as the half-hour point was nearing, but Martinez was finding it hard to score.
The captain missed the cross from Hakan Calhanoglu, who came in from a tricky angle.
Subsequently, a goal he had scored was disallowed as Barella was offside. He also did not receive a corner after Strahinja Pavlovic deflected his shot wide. Finally, he went off-target.
The Rossoneri then built a threat of their own, with Tijjani Reijnders' attempt needing a good save, before Benjamin Pavard intervened with a good tackle to stop Rafael Leao from getting to the Dutchman's pass.
They did not, however, relent before the break, with Yann Sommer getting a touch on Leao's low cross but only able to push it to Reijnders for the midfielder to score first.
Careless play presented Inter with a great opportunity inside a minute of the resumption, yet Martinez fired directly at Maignan.
Shortly afterwards, a quick break concluded with Denzel Dumfries blocking a shot from Leão as the second half got off to a rapid start.
Fikayo Tomori then leaped as high as Stefan de Vrij to head his header behind, prior to a Dimarco shot being blocked.
Simone Inzaghi responded by substituting three players in the 63rd minute, but Inter were left with the same infuriating trend as Martinez's goal was again disallowed.
Yann Bisseck headed the ball and it bounced off the post, and Henrikh Mkhitaryan wide before Reijnders' poor shot was blocked.
The post rescued Milan again by preventing efforts from Marcus Thuram and Dumfries. Maignan rushed out afterward to block Dumfries.
Inter refused to give up. New arrival Nicola Zalewski chested it down to De Vrij, who scored immediately. That kept Inter's unbeaten streak in Serie A going for 17 matches, the longest ongoing run in the league.
While not a loss for Milan, to lose so late is another disappointing setback after their midweek loss to Dinamo Zagreb.