The Latics, forced to play with 10 men for 70 minutes following the sending-off of Jean Yves M'Voto, went ahead after 67 minutes when Jose Baxter fired in following an assist by Lee Croft.
But Crawley, who also lost midfielder Hope Akpan to a straight red card in the second half, equalised 11 minutes from time through McFadzean, who unleashed a low drive from 25 yards after Nicky Adams had played on a short corner by Sergio Torres.
M'voto was sent off for shoving McFadzean in the face before pushing over skipper Gary Alexander after the ball had gone out of play for an Oldham corner.
Billy Clarke went close for Crawley early on by putting an angled drive wide and seeing a deflected shot go behind for a corner.
McFadzean should have hit the target shortly before the break when he blazed over after a fierce shot by Adams was blocked, while Crawley midfielder Akpan received a straight red card after 62 minutes following his a heavy challenge on Robbie Simpson.