United were undone by former striker Leon Clarke as they crashed to a 2-1 defeat at the hands of Coventry City at Glanford Park.
City, who appointed Steven Pressley as manager on Friday, extended their unbeaten run away from home to six matches.
The former United loanee, Clarke, headed home the winner with 13 minutes remaining as he escaped his marker to head past a stricken Eirik Holmen Johansen, who was making his Iron début.
Clarke, who scored both of the Iron's goal in the 2-1 victory at the Ricoh Arena earlier in the season, climbed above captain Paul Reid before heading the ball just inside the left-hand post.
Winger Andy Barcham could have given the home side the lead inside two minutes when the ball fell to him six yards out, however, he could not get his shot on target.
Jimmy Ryan then forced former Iron goalkeeper Joe Murphy into another save after his shot hit the 'keeper and went behind for a corner.
The Iron then opened the scoring on eight minutes when Akpo Sodje rose the highest at the far post to head home his fifth goal for the club past a helpless Murphy.
The build up play was patient from United down the right flank between Mark Duffy and Eddie Nolan. It was then the latter of those two players who sent in the floated ball into the box to give United an early lead.
In a first 15 minutes dominated by the home side, the Iron came close to doubling their lead when Karl Hawley rounded Murphy to the by-line before unleashing a shot that crashed back off the near post.
Coventry defender William Edjenguele got let off the hook by referee Tony Bates when he waved away a foul on Barcham when he was clean through on goal. The United players surrounded the match official, however, he was never going to change his decision.
Franck Moussa came close for the visitors just before the break when his shot from the edge of the area went several yards wide of the goal.
United's new goalkeeper, Eirik Holmen Johansen, could do nothing about Coventry's equaliser which came on the stroke of half-time courtesy of Carl Baker's shot that skimmed through a crowded box -wrong footing the six foot four inch goalkeeper.
Baker - who scored the opening goal in the reverse fixture at the Ricoh Arena - saw his shot nestle in the back of the net after squeezing through a crowded box.
The Iron started the second half brightly, just like they did in the first. Sodje could have restored United's lead but his back heel - from three yards out - went straight into the hands of Murphy.
On the hour mark, Leon Clarke marked his return to Glanford Park when he found the back of the net in typical style. He rose above Paul Reid before heading the ball into the ground and past Johansen. However, the assistant referee was quick to raise his flag for offside to the delight of the home support.
Moussa - a former Doncaster Rovers and Chesterfield loanee - attempted to give the visitors the lead for the first time. However, he got his connection all wrong and it skimmed across the ground and harmlessly away from goal.
Duffy attempted to recreate the goal he scored in the 1-0 home win over Stevenage. The United right-winger cut in from the right - onto his left foot - before shooting but Murphy got his body behind the ball.
With United in dire search of an equaliser, Ryan shot from 25 yards forcing Murphy to claw the ball out of the top corner and out for a free kick.
The resulting corner never threatened the City defence as James Alabi's header cleared the crossbar.
In added time United had two chances to steal a point from their visitors. Firstly Alabi's header was deflected over the bar before Nolan's low drive was straight at Murphy, who initially spilt the ball before claiming the ball at the second time of asking.
With the last attack of the match United manager Brian Laws sent up 'keeper Johansen for Duffy's corner. However, the United winger decided to play a low ball out to Ryan instead of floating one onto the head of the goalkeeper-come-striker.
Scunthorpe United: Johnansen, Nolan, Mirfin, Reid, Newey, Duffy, Ryan, Collins, Barcham (Jennings, 85), Hawley, Sodje (Alabi, 73)
Substitutes: Severn, Ribeiro, Walker, Grella, Canavan.
Coventry City: Murphy, Dickinson, Christie, Edjenguele, Martin, Baker (Willis, 90), Jennings, Moussa, Bailey, McSheffrey (Fleck, 77), Clarke
Substitutes: Dunn, Stewart, Thomas, Bell, McDonald.
Attendance: 3,676 (723 away).
Iron Bar man of the match: Akpo Sodje.
Sponsors man of the match: Mark Duffy.