Chris Lucketti headed Preston in front before half-time when Gabor Kiraly failed to catch Paul McKenna's corner.
Danny Dichio was the first to see red for raising his arm at Morrison, and Claude Davis followed for a challenge on Dougie Freedman four minutes later.
Preston manager Billy Davies
"I asked the referee to look at the video of the game and assess his own performance, because his decisions were very, very poor.
"I've seen both red cards, and neither of them were justified. What's more Palace boss Iain Dowie agreed with me.
"Games like these depend on referees being strong."
Crystal Palace: Kiraly, Ward, Butterfield, Boyce, Soares (Reich 71), McAnuff, Watson (Hudson 85), Riihilahti (Freedman 42), Hughes, Borrowdale, Morrison.
Subs Not Used: Andrews, Speroni.
Goals: Morrison 90.
Preston: Nash, Alexander, Davidson, Davis, Lucketti, Jones, Sedgwick (Etuhu 73), McKenna, Lewis Neal (Hill 72), Nowland (Agyemang 66), Dichio.
Subs Not Used: Lonergan, Mears.
Sent Off: Dichio (63), Davis (69).
Booked: Lucketti, Jones, Nowland, Sedgwick.
Goals: Lucketti 43.
Att: 17,291
Ref: S Tanner (Somerset).