Scott Pittman scored a stoppage-time winner in Belfast to send League One side Livingston into the quarter-finals of the Scottish Challenge Cup.
After a low-key first half, Livingston took the lead with substitute's Josh Mullin's first touch.
Crusaders, Irish Premiership champions for the last two seasons and current leaders, equalised with a fine shot by their record scorer Jordan Owens.
But Pittman grabbed the winner in the third minute of added time.
He directed a shot into the bottom corner after Liam Buchanan had pulled the ball back.
It was a harsh end for the Belfast side who looked to have forced extra-time through that Owens equaliser which came with just two minutes of normal time left.
Declan Caddell picked out the Crues striker who curled a superb shot past Livi keeper Gary Maley.
The other Irish Premiership side in the competition, Linfield, play Queen of the South on Sunday.
What they said
Crusaders manager Stephen Baxter: "To concede with the last kick of the ball was difficult because we had all the pressure and I thought we could be heading towards the next round.
"They are a big solid side and broke up the pitch very quickly.
"In the second half we got a grip of the game and after the match I told the players how pleased I was with their performance."