United were defeated 1-0 by Brentford at Griffin Park on Saturday afternoon.
Substitute Tom Adeyemi scored with his first touch of the game on 70 minutes to hand all three points to the Bees after a game which had seen the two sides evenly matched up to that point.
The Iron entered the game making no changes from the side that won against Stevenage in midweek.
Sam Slocombe started in goal, with Eddie Nolan, David Mirfin, Niall Canavan and Tom Newey forming the defence.
The midfield consisted of Jimmy Ryan
, Josh Walker, Michael Collins and Andy Barcham, with Mark Duffy supporting Karl Hawley in attack.
The substitutes were James Severn, Christian Ribeiro, James Alabi, Mike Grella, Hakeeb Adelakun, Matt Godden and Connor Jennings.
The game got off to a bright start, with Scunthorpe having the first chance on four minutes when a Duffy cross from the right wing found the head of Barcham, who directed his effort over the crossbar.
Then, in the seventh minute, Ryan was next to come close as his right-footed free-kick from 25 yards fizzed just wide of goal.
The Bees had their first real chance in the tenth minute when Marcello Trotta's low powerful effort drew a stop from Slocombe, who tipped around his left hand post.
With 20 minutes on the clock, he was next to come close again - this time driving down the right side of the area before rifling a powerful low shot which Slocombe had to be alert to stop.
A minute later, Walker clipped an effort well over the crossbar after good wing play by Duffy.
On 22 minutes, Nolan managed to bundle his way into the area and drove forward before shooting just over the crossbar.
In the 30th minute, Scunthorpe continued to press and frustrate the home support in turn. Canavan just failed to get on the end of a Duffy free-kick delivery as the visitors continued to have the better of the game.
On 35 minutes, Bradley Wright-Phillips drew a superb save from Slocombe, who clawed away the striker's header, diving low down to his left.
As half-time approached, the hosts pressed but Scunthorpe defended resolutely against their crosses into the box and, on 44 minutes, Nolan got forward before fizzing a powerful drive into the arms of the Bees goalkeeper.
The Iron were quick out of the blocks in the second half, and Newey managed to get down the left flank and sent in a great cross which Hawley just failed to get on the end of.
Then, at the other end, Trotta sent an attempt well wide.
Slocombe was then forced into a save in the 51st minute as Hawley cleared a corner as far as Jonathan Douglas, whose side footed volley was stopped by the Scunthorpe custodian.
Both sides looked threatening at the start of the second period, and Duffy was next to come close as his free-kick from the left flank just clipped the top netting.
Then, on the hour mark, Collins delivered a great cross from the right flank which Barcham gambled on but just failed to get a connection to it.
The hosts took the lead on 70 minutes as a goalmouth scramble following some Bees pressure resulted in substitute Adeyemi sidefooting beyond Slocombe from 12 yards.
A United alteration was made in the 75th minute as Alabi replaced Walker to add an extra threat to the attack.
Former Iron defender Shaleum Logan was next to fire an attempt towards goal but his effort drifted over the crossbar.
Then, Wright-Phillips bundled wide from close range after Harlee Dean's flick on as the hosts threatened to double their lead.
On the counter-attack after Hawley's effort was blocked, Trotta tested Slocombe again with a toe-poked effort but the United goalkeeper parried away.
Former Bees man Grella came on for Barcham with ten minutes left as Scunthorpe looked to pep up their attack, while Jennings then came on for Hawley in the closing stages.
And the two substitutes almost combined with an instant effect on 87 minutes as Jennings' flick on found Grella, whose rifled drive was parried away by the Bees goalkeeper.
There were five minutes of stoppage time but Duffy's drilled volley wide in the third of those minutes proved the last action of note for the Iron as they suffered defeat at Griffin Park.
Scunthorpe are next in action on Saturday when they host Coventry City.
Moore, Craig, Dean, Saunders (Dallas, 60), Douglas, Trotta, Logan, Wright-Phillips, Forrester (Bidwell, 80), Reeves (Adeyemi, 67), Moore.
Substitutes not used:
Lee, Barron, Diagouraga, Hayes.
Slocombe, Nolan, Mirfin, Canavan, Newey, Ryan, Walker (Alabi, 75), Collins, Barcham (Grella, 80), Duffy, Hawley (Jennings, 87).
Substitutes not used:
Severn, Ribeiro, Adelakun, Godden.
5,400 (337 away).