Leeds (8) 26
Tries: Hall, Smith, Donald, Delaney Goals: Sinfield 5
Crusaders (12) 32
Tries: Mellars 2, Peek, Hauraki 2 Goals: Schifcofske 6
Crusaders winger Mellars took his try haul for the season into double figures
Brian Noble's Crusaders pulled off one of the shocks of the season at Headingley to end champions Leeds's seven-game winning run.
Winger Vince Mellars won it for the visitors with his second try of the game just two minutes from time.
Second row Weller Hauraki also scored twice for Crusaders, now buoyant after ending the poor run that followed last month's last-minute Challenge Cup exit.
The Rhinos scored four tries to the visitors' five as they succumbed.
Adam Peek got Crusaders' other try, while Lee Smith, Scott Donald and Brett Delaney all ran in second-half tries for Leeds, to add to Ryan Hall's first-half effort.
But, after being pegged back to 26-26 by Delaney's converted effort with only four minutes left, Crusaders had the strength of character to return to the other end and win it.
The Welshmen had already caused a stir by beating Bradford - the club where Noble enjoyed so much success as coach - for the second time this season last weekend.
But this one reversed the 34-6 defeat Crusaders suffered against the champions on the opening night of the season back in January, to push Noble's men right into contention for a top-eight finish.
To add to Leeds' woes, prop Kylie Leuluai sustained a leg injury which forced him off in the second half.
When the Rhinos led inside the third minute after Hall's pace and strength took him over in the left corner, it looked to be the signal for another rout.
But Crusaders levelled on 27 minutes when hooker Lincoln Withers' neat short offload found scrum-half Rhys Hanbury and he showed impressive pace to glide past two Leeds players before sending Mellars over with a perfect inside pass.
Clinton Schifcofske added the extras for the first of his six goals and, six minutes later, the visitors struck again when a simple short offload from Lloyd White sent fellow replacement Peek crashing over from close range.
Kevin Sinfield kicked a penalty on the stroke of half-time to cut Crusaders' lead to four points, but six minutes after the restart Jordan James' neat offload sent Hauraki bustling over.
Schifcofske landed his third goal but Leeds responded in style as Smith showed real desire to force his way over in the right corner and then Danny McGuire orchestrated a fine move which culminated in Scott Donald going over in the same spot.
Sinfield, who ended with five goals, converted both tries to edge Leeds 20-18 ahead but the loss of Leuluai was a blow to the home side.
And a penalty from Schifcofske drew Crusaders level before Hauraki took a pass from Mark Bryant and sauntered over.
Delaney then found the space to cross for a try which Sinfield converted to tie it up again at 26-26.
But the drama was not over and there was still time for Mellars to weave his way over to earn Noble's Crusaders arguably their finest hour.
Rhinos coach Brian McClennan said:
"We weren't really at the races. I don't want to say too much because that would disrespect Crusaders. They deserved to get the points today.
"They worked hard and got the job done, so well done to them.
"We've got to take it on the chin and move on because we've got a big game coming up against Warrington next weekend."
Crusaders coach Brian Noble said:
"I love this stadium. It's a fabulous place to come and play rugby.
"We instilled the belief in the players and I thought we deserved to win.
"We had a good win against Bradford last week after a poor run and we backed our efforts up, which was extremely pleasing.
"There was a belief about us today and I'm extremely pleased for the players. But we need to kick on from here now."
Leeds: Smith, Donald, Delaney, Senior, Hall, Sinfield, McGuire, Leuluai, Buderus, Peacock, Eastwood, Ablett, Clarkson.
Replacements: Kirke, Jones-Buchanan, McShane, Bailey.
Crusaders: Schifcofske, Youngquest, Martin, Mellars, Dyer, Lupton, Hanbury, O'Hara, Withers, Bryant, Hauraki, Chan, Winternstein.
Replacements: Peek, James, Flower, White.
Referee: R Hicks (Oldham)