Simon Grayson's side scored three goals in 12 first-half minutes and a fourth two minutes from time to warm up for their FA Cup third-round replay against Arsenal in midweek by securing three more points in their bid to return to the top flight.
Sanchez Watt's first goal for the club put the Whites on their way and further strikes from Max Gradel, his ninth of the season, Bradley Johnson and Davide Somma confined sorry Scunthorpe to a ninth defeat in their last 10 games.
Leeds, on the other hand, have lost just one of their last 15 matches in all competitions and, on this evidence, Arsene Wenger's side will have their work cut out on Wednesday night.
Scunthorpe set out to stifle Leeds with new signing Abdisalam Ibrahim and Sam Togwell shielding the back four.
But Grayson's side burst into life with three goals in the space of 12 minutes to stun their struggling rivals.
On-loan Arsenal forward Watt got the ball rolling 16 minutes in, when he fed on a flick-on from Luciano Becchio and spun Paul Reid before rifling a left-foot drive which goalkeeper Joe Murphy got a hand to but failed to prevent from finding the bottom-right corner.
Scunthorpe were caught napping three minutes later when the impressive Robert Snodgrass sent Gradel racing clear of the Iron defence, and the former Leicester man produced a moment of class by casually rounding Murphy before tucking the ball into an empty net.
Leeds were brimming with confidence and added a third goal after 28 minutes when a tricky Snodgrass embarked on mazy run. And despite being stopped in his tracks by two Scunthorpe defenders, Johnson drove home the loose ball with a venomous left foot strike.
Scunthorpe almost pulled a goal back before the break when Michael Collins was first to Martyn Woolford's left-wing cross, but his effort looped wide at the far post.
Watt's movement was causing Scunthorpe all kinds of trouble, and three minutes into the second half he found space in the penalty area but Murphy palmed away his right-foot strike.
And on-loan Leeds left-back George McCartney deserved better when his surging run and cutback evaded the onrushing Billy Paynter.
Substitute Jonathan Forte was unfortunate not to grab a consolation eight minutes from time after displaying some lovely skill before seeing a right-foot drive deflect off Alex Bruce and strike the crossbar.
And to add insult to injury for Scunthorpe, substitute Somma fired home a fourth goal from the angle with a clinical right-foot finish two minutes from time.