But the determined visitors fought back to equalise through on-loan Jack Cork - whose dad Alan is a former Coventry reserve team manager.
Coventry dominated possession in the first half without failing to make their chances count against a team who had lost their last three matches.
In an excellent move, Scunthorpe's Youga - playing out-of-position at right-back - was unable to prevent Stephen Hughes' fine pass reaching Julian Gray.
The midfielder took the ball to the byline before sending over a cross which Leon McKenzie headed over the bar.
The talking point of the first half arrived in the 31st minute when referee Mike Jones awarded the Sky Blues a penalty - only to change his mind.
The Cheshire official pointed to the spot after Tabb appeared to be fouled inside the box by Youga, but after talking to his linesman, Jones awarded Coventry a free-kick on the edge of the box and McNamee sent the chance flying past the far post.
But Jones didn't change his mind a second time in the 51st minute.
Tabb outpaced centre-half Andy Butler after latching onto McKenzie's pass and, as he rounded the keeper, the midfielder was hauled down by Murphy.
The keeper was shown a red card and there were no heroics from substitute keeper Josh Lillis, who was emphatically beaten from the spot by Doyle.
In front of the lowest ever league crowd at the Ricoh Arena, the Iron nearly equalised in the 58th minute when Jim Goodwin's 20-yard free-kick rattled the bar.
Nigel Adkins' men drew level ten minutes later when Marcus Williams' cross from the left was thumped home by Cork from inside the box.
Scunthorpe were reduced to nine men in the 83rd minute when Youga was sent off for picking up his second yellow card in two minutes after being penalised for persistent fouling and then for dragging back substitute Ellery Cairo.