Zachary Athekame's long-range shot in time added on earned the Serie A leaders a last-gasp 2-2 draw, as promoted side Pisa almost escaped with all three points on Friday.
Milan lead Serie A on 17 points but Inter, Napoli and Roma are all on 15pts ahead of their games this weekend.
Pisa narrowly missed a famous win after starting the game rock-bottom of the league and falling behind to a seventh minute goal from Rafael Leao.