The Reds are currently 11 points adrift of the top four and Irwin insists three points is a must against Tony Pulis' in-form Eagles.
"If we have any designs on finishing fourth, we have to start winning games and putting pressure on teams above us," Irwin told ManUtd.com.
"Palace won't be easy though. Tony Pulis has done unbelievably well since he took over [in November] and has got them playing with a lot of confidence.
"I'm sure many people wrote them off two or three months ago, given how they were struggling since stepping up from the Championship. But since he's taken over he's done a fantastic job and it'll be a really tough game for us. But it's one we have to win. It's as simple as that."
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