McManaman, who came under fire for a wild studs-up challenge on Newcastle’s Massadio Haidara in 2013, jumped at fellow substitute Claude Dielna with both feet in the 68th minute to earn his marching orders and Wednesday promptly took full advantage.
Atdhe Nuhiu nodded beyond Wigan goalkeeper Scott Carson nine minutes after McManaman’s rush of blood to the head as the hosts suffered a third straight home loss, with Mackay having taken just one point from the 12 on offer at the DW Stadium since his controversial appointment last month.
For an awfully long time the game was devoid of quality, though, as both sides struggled for rhythm and were unable to work any clear-cut openings.
Lewis McGugan poked the ball away from winger-cum-striker James McClean inside the Wednesday area, while Rob Kiernan’s error allowed Jacques Maghoma to fizz in a cross which Nuhiu would have bundled in had Ivan Ramis not got back to snuff out the danger on the line.
Tom Lees and McGugan both fired wide, the latter via a Kiernan deflection, while Latics were again denied by late interventions as Joe Mattock flicked the ball away from Marc-Antoine Fortune’s head at the back post.
McClean tried to up the ante after the interval by racing away down the left and forcing goalkeeper Keiren Westwood into his first action of the evening, and Ben Watson should have done better when heading off target from the resulting corner.
Mackay brought on McManaman and midfielder Roger Espinoza, who was likely making his farewell appearance, and they did have the ball in the net just before the hour as McClean diverted Watson’s free-kick inside the near post, only for the goal to be chalked off for offside.
Wigan had hoped McManaman’s introduction would liven up proceedings and the 23-year-old did just that, although not in the way Mackay had banked on.
He lunged two-footed at Dielna’s heels from behind to earn the second dismissal of his career following last year’s red at Bournemouth and leave his team-mates with an uphill task.
Straight away Wednesday pushed on and although Carson denied one Nuhiu header, he was unable to stop the towering striker 77 minutes in.
Jeremy Helan’s left-wing cross looped into the air and the big Austrian directed the ball beyond Carson’s left hand in front of the travelling support.
Chris Maguire almost cashed in when Carson went racing out but it was the home side who would come closest to grabbing the game’s second goal.
Substitute Shaun Maloney’s free-kick from the left went past everyone and came back off the inside of the post, with McClean firing the rebound over on another disappointing DW Stadium evening for Latics.