Nottingham Forest's Garath McCleary struck four times as Leeds conceded seven goals at home for the first time.
Robert Snodgrass put Leeds ahead with an early penalty but Forest hit back with goals from Adlene Guedioura, McCleary and Dexter Blackstock.
Luciano Becchio and Michael Brown pulled Leeds level only for McCleary to strike three times in the space of 15 minutes to stun the home side.
Blackstock struck his side's seventh to help Forest's battle against the drop.
Forest manager Steve Cotterill labelled his side's win an "unbelievable game" as they astonishingly scored seven times against a Leeds defence who had conceded just a miserly two in five games since Neil Warnock took charge.
But there was little sign of things to come when Ross McCormack was brought down by Guedioura and Snodgrass scored from the spot to put Leeds ahead after just six minutes.
The home side barely had time to celebrate before on-loan midfielder Guedioura atoned for his mistake by producing a stunning 35-yard strike to equalise.
Winger McCleary, who went into the match with nine goals in 117 games, had proved a constant threat to Leeds and put the visitors ahead as he finished off a Forest counter-attack with a right-foot shot just before the break.
Leeds were booed off at half-time and they did little to appease their fans when Blackstock headed in an Andy Reid cross to extend Forest's lead.
Becchio slotted in and Brown produced a half-volley to level for Leeds with two goals in as many minutes but the home side soon let their good work go to waste.
The Leeds defence was proving vulnerable and McCleary took advantage with three goals in quick succession.
He latched on to a Blackstock flick to drill in a shot, slotted in an effort after being set up by Reid and produced a measured finish to take his tally to four for the game.
Forest had been on the end of 4-0 and 4-1 drubbings from Leeds in the two prior fixtures but they gained retribution in emphatic manner when Blackstock scored a seventh.
Despite the defeat, Leeds remain five points from the play-off zone, while Forest are seven points above the relegation zone.
Leeds United manager Neil Warnock:
"I'm quite embarrassed about the result.
"But I don't think you learn much about your players when you're winning games, I think you learn things when things go against you, who stands up and who you want in the trenches with you.
"I've learnt probably more than I have in the other games, but in fairness some of them were just shattered."
Nottingham Forest boss Steve Cotterill:
"Garath McCleary comes from non-league. He's a special talent, he's raw, he's got two good feet, he can head it, he's strong. I think he can go on to be even better, I think he's a top lad.
"It was a stunning game, I know we've won but Leeds United played their part as well. Our chances went in, but they played their part.
"I thought it was an outstanding game by both teams. We're very pleased with the three points more than anything else, but to play in the manner we've played, we've done that a lot this season and ended up losing 1-0 so maybe it's evened out a little bit."