The reward for Stephen Baxter's men is a home tie against Glenavon on Saturday 9 February.
The first chance of note at Seaview came on 12 minutes and it was Linfield who failed to make it count when a Michael Carvill free kick fell to Matthew Tipton at the back post but the normally lethal finisher lashed the ball high over the bar.
Crusaders hit back with a good spell with a couple of testing moves well dealt with by the Linfield back line but Timmy Adamson did go close with a glancing header from a throw-in by McKeown on 21 minutes.
The first save of the game came on 23 minutes and Craig Hyland on his Crusaders debut did well to push away a firmly hit free kick by Michael Carvill.
Hyland was soon picking the ball out of the net as Linfield took the lead on 27 minutes and it was a real screamer from Brian McCaul which flew into the top corner.
With no one picking up the Linfield striker he and time and space to go for goal and he did so in some style to record his 14th goal of the season.
Carvill was then given a yellow card for diving as the keeper raced out to block his angled run in the box while at the other end Paul Healty rounded BJ Burns with ease but then fired his parting shot high over the bar.
The Crues were level on 37 minutes from the penalty spot after Albert Watson chopped down Adamson in front of referee Colin Burns. Watson picked up a yellow card and there was more pain for the Blues as Gary McCutcheon sent Ross Glendinning the wrong way from the spot.
The home side made a lively start to the second half and almost caught the Blues napping as McCutcheon tried to connect with a Heatley cross but his touch was too heavy. The busy Caddell got on the end of a McKeown lob into the box but Glendinning was equal to it.
Crusaders brought on another striker with Jordan Owens replacing Chris Morrow on 62 minutes but it was defender David Magowan with a thumping drive from 30 yards which Glendinning had to contend with.
The Linfield keeper made an even better save a few minutes later tipping away a shot from Robinson. Then the woodwork saved the Blues with McClean's shot clipping the bar.
The Crues were in command at this stage and it was no surprise when they took the lead on 69 minutes. Owens crossed, Heatley miskicked but the ball was rifled home by Adamson.
It was almost 3-1 for the Crues when a flowing move saw Caddell cross for Heatley but his half volley flew inches over the bar.
Substitute David Rainey should have scored when through but the keeper did well to block his shot near the end.
Linfield can have few complaints, the Crues deserved go through especially with their second half performance.
Crusaders last won the cup in 2009 but lost the last two cup finals to the Blues.