The 20-year-old phenom scored his league-leading 10th goal of the season to save a point for Philly.
Toronto's Doneil Henry was sent off in the 41st minute. He had been carrying a yellow card from an earlier back-and-forth with Union keeper Zac MacMath, and was shown a second after a tackle on Danny Cruz.
Jonathon Osorio scored for TFC in the 66th minute. Catching the Union defense sleeping, Jeremy Brockie curled in a cross from the end line and found Osorio. Leaping, he beat Amobi Okugo to the ball and slammed home a powerful header past MacMath.
McInerney equalized in stoppage time. Hanging back from a corner kick, he collected a clearing header and rifled a shot into the far low corner to make it 1-1 and steal a largely undeserved point.