McCormack fired his 14th and 15th goals of the season to put Leeds on the fringes of the Championship play-off places as managerless Wigan slipped to a fourth straight defeat.
Leeds striker McCormack bundled home his seventh goal in five matches in the 15th minute and then saw his 77th-minute free-kick curl inside the far post for a game-clinching second to lift Brian McDermott’s side up to seventh place in the table.
Wigan, whose manager Owen Coyle offered his resignation after Saturday’s home defeat to Derby before parting company with the club “by mutual consent” on Sunday, were by no means overrun.
Wigan caretaker-boss Graham Barlow made five changes for his first game in charge, but the visitors were still a shadow of the side that held their own in the Barclays Premier League for eight years before relegation in May.
While Leeds skipper Rudy Austin drove his side towards a fourth win in their last five league matches, Wigan have won only two of their last seven in the Championship.
Leeds midfielder Luke Murphy rifled an early shot straight at Wigan goalkeeper Scott Carson, making his first appearance since October following an ankle injury.
The home side made just one change – striker Matt Smith in for Luke Varney – and were quicker to settle, opening the scoring in the 15th minute via leading goalscorer McCormack.
Defender Jason Pearce headed on teenager Alex Mowatt’s corner and McCormack bundled the ball home from close range.
Smith, 6ft 6in, caused the Wigan defence problems every time the ball was played into their penalty area and his header from Mowatt’s curling cross was blocked just short of the goal-line.
Wigan striker Will Keane went close to equalising for his side twice in as many minutes midway through the first half, but was bravely thwarted on each occasion by Leeds keeper Paddy Kenny, who first beat him to a ricochet and then brilliantly blocked his point-blank snap-shot.
Leeds defender Marius Zaliukas diverted Nick Powell’s header as Wigan probed for an opening and from Jean Beausejour’s subsequent corner skipper Emmerson Boyce was unable to steer his first-time shot on goal.
Barlow sent on striker Grant Holt and midfielder James McClean for Keane and Beausejour 10 minutes into the second half and their introduction lifted the visitors, with Powell heading Ben Watson’s corner just off target.
At the other end, Leeds defender Tom Lees blasted a shot wide following a goalmouth scramble and Carson did well to beat away McCormack’s fierce drive.
Barlow had by then sent on his third substitute, winger Callum McManaman, but Leeds went close again when Smith’s towering header from Pugh’s fine cross spun wide of Carson’s left-hand post.
Leeds then spurned a golden chance to effectively tie up all three points.
Smith robbed dithering Wigan defender Ivan Ramis in the centre circle and with the visitors’ defence caught square, the big striker chose to shoot when one-on-one with Carson, despite both having Murphy and McCormack on either side, and his shot was smothered by the keeper.
But Leeds gave themselves some breathing space in the 77th minute.
McCormack swung over a free-kick from the left and although Pearce reacted quickest and appeared to get the faintest of touches, replays showed the ball evaded everybody before bouncing beyond Carson and the home side comfortably held out for their fifth straight home win.