Paul Hayes eased Scunthorpe's relegation fears and dealt Sheffield United's Coca-Cola Championship play-off hopes a huge blow as his goal in first half stoppage time secured a 1-0 win.
Iron striker Hayes swept home Donal McDermott's cutback in time added on at the end of an uneventful first period to condemn Kevin Blackwell's patched-up Blades to only their third home league defeat of the season.
The Blades, with seven first-team players still sidelined through injury, have now won only one of the last seven league games and trail sixth-placed Leicester by seven points with six games remaining. Scunthorpe have climbed eight points clear of the drop zone thanks to Hayes' 12th goal of the season, which secured Nigel Adkins' side a third straight league win.
Iron defender David Mirfin rescued the visitors in the 20th minute when he blocked Paul Connolly's shot on the goalline and Mark Yeates headed over from Richard Cresswell's shot soon after.
The Blades were given a big let-off in the 31st minute. Nyron Nosworthy's back pass was woefully short and visiting striker Garry Thompson pounced to race clear on goal, only to fire straight at goalkeeper Steve Simonsen.
The home fans' impatience turned to jeers of derision as Scunthorpe midfielder McDermott wriggled his way into the area and set up Hayes, who steered the ball underneath Simonsen from eight yards for an unlikely breakthrough.
Yeates' free-kick, after Grant McCann had tripped Quinn on the left corner of the area, forced visiting goalkeeper Joe Murphy into a smart save 10 minutes after the restart.
Blades defender Kyle Bartley headed Connolly's free-kick over the crossbar in the 64th minute as the home side stepped up the tempo, but Scunthorpe almost doubled their lead soon after, with Thompson bursting on to McDermott's through-ball and forcing Simonsen into a fine save.
Referee Russell Booth then waved away Scunthorpe's penalty appeals when substitute Jonathan Fortune went tumbling in the box, while Henderson's header from Montgomery's ball in grazed the Iron crossbar.
Blackwell's men huffed and puffed in the closing stages, but lacked the cohesion to open-up a determined Scunthorpe rearguard despite five more minutes of time added on.
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