The assistant referee spotted the big striker laying an elbow into Palace defender Mark Hudson and referee Rob Styles followed that with a red card.
Despite going down to ten so early on, Leeds continued with a positive attitude and indeed were the better side in the first half. But Palace upped the tempo after the break and just when it looked Leeds would hold out for a point, Morrison swooped a minute into injury time.
Mark Kennedy played a decent ball into the box where Leon Cort got a head to it and it fell nicely for the Irish international, a sub of barely 15 minutes, to fire home from just eight yards out.
The first half saw Palace making real hard work of it and indeed Leeds should have gone in front. Eddie Lewis clipped the outside of the post but the unlucky man in the first half was David Healy.
He had four or five useful chances to fire his side in front as Leeds were not afraid to attack.
Despite being one man down, Leeds had a great chance in the second half, but Shaun Derry sent a free header over the bar.
It was Dougie Freedman who made the difference for Palace. He came on at half-time to replace Ben Watson and could have scored within minutes when coming on the field, but shot straight at Tony Warner who made his first save of the game.
And then five minutes from time, Freedman cleared the Leeds defence that was caught square and the Scotsman fired a great shot from 15 yards out, but Warner magnificently tipped over the bar to keep Leeds still in the game, but it was not to be.
Just when perhaps Leeds thought they had done their job, Morrison struck to ensure Palace stayed top of the table.