Cliftonville moved nine points clear at the top of the Irish Premiership with a game in hand thanks to an 80th-minute goal from substitute Joe Gormley.
The Reds striker fired into the bottom corner with Crusaders players appealing in vain for an offside flag.
The Crues had enjoyed the better of the chances, with Timmy Adamson missing two good chances and Colin Coates heading over the bar from three yards out.
The north Belfast derby was played in front of a capacity crowd at Solitude.
Crusaders had the better of the first half and Gary McCutcheon had the ball in the net, but his effort was ruled out for offside.
Adamson fired into the sidenetting with just goalkeeper Conor Devlin to beat after some poor defending by the home side.
In the second half, Sean O'Neill denied Liam Boyce and Devlin saved a Declan Caddell header.
Adamson then mis-hit a shot, allowing O'Neill to gather easily, and defender Coates should have scored for the Crues.
Following his introduction from the bench, Gormley was wide with an effort but found his range to strike home the winning goal, to the delight of the large home support.
"We were not at our best, but it was good to get the result in front of a big crowd - we maybe had a bit of luck with the offside decision, but these things tend to even themselves out over the season," said Reds manager Tommy Breslin after the game.