A scruffy goal from Conor McAleny midway through the second half gave Wigan Athletic a potentially priceless three points against Rochdale.
Latics had found the going tough against their north-west neighbours, despite playing for an hour with an extra man following the first-half sending-off of Ian Henderson for lashing out at Jason Pearce.
They squandered numerous opportunities to go in front, and looked like the chance to move to within a point of long-time leaders Burton would slip through their fingers.
But they finally got the breakthrough at the three-quarter mark, with a goal as scrappy and fortuitous as it could prove to be important.
After a Yanic Wildschut shot had been deflected on to the bar, the flying Dutchman saw his follow-up parried by goalkeeper Josh Lillis.
The ball then rolled across the six-yard box and looked like it was going to be cleared by a desperate defender.
However, McAleny managed to get himself in the way, and the ball was somehow forced home by a mixture of the on-loan Everton striker and the unfortunate Dale man.
In truth, Latics should have been out of sight by that point, but they showed a quality often possessed by promotion-winning sides in getting the job done when not being at their best.
The result extends Wigan’s unbeaten run to 18 matches, and sees the gap to third-placed Walsall stretched to six points with seven matches to go.
Looking to steal a march on their rivals thanks to the early kick-off, Latics could and perhaps should have gone ahead with only three minutes gone.
Stephen Warnock’s cross from the left was left by Will Grigg only for Ryan Colclough to side-foot well over the top from 10 yards.
To their credit, Rochdale also started on a positive note, aiming to maintain their fine recent form that has seen them become unlikely play-off contenders.
Nathaniel Mendez-Laing looked to have got the wrong side of Craig Morgan, who stuck to his task and eventually got a foot in.
There was a huge shout for a Latics penalty on 12 minutes when Reece Wabara’s cross found its way to Wildschut, whose goalbound shot clearly hit the hand of a defender.
However, the Dale man was standing at such close proximity that the official was probably within his rights to wave play on.
Sam Morsy was the first Wigan man to work the Dale goalkeeper, who did well to parry away a low shot from 25 yards.
At the other end, Donal McDermott’s effort from a similar distance was straight at Jussi Jaaskelainen.
David Perkins was again in fine form for Latics, and the midfielder threatened to notch his first goal for the club after advancing into the box, only for his shot to be deflected wide.
Perkins was then forced to take a yellow card for the team as Dale broke, and was perhaps fortunate to escape further action with a couple of other indiscretions that, on another day, could easily have brought about a second caution.
However, when the red card did come, on the 32-minute mark, it was the visitors who were reduced to 10 men.
Henderson was initially the victim after being wiped out by a crude lunge from Pearce right in front of the technical areas.
But the Dale man completely lost his head and lashed out at Pearce, and can surely have had no complaints at seeing the official brandishing the inevitable red.
Pearce was awarded only a yellow for his foul, which did little to pacify the onlooking Dale bench.
From then on it was attack against defence, with the visitors retreating into a 5-4-0 formation and trying to make the most of any set-pieces that came their way.
Latics almost broke through just before the break, when Wildschut glided through a couple of would-be challenges before being crowded out.
The ball fell to Colclough, whose shot was blocked, with Max Power’s follow-up receiving similar short shrift.
Power’s corner found Pearce at the near post, but the big defender couldn’t make a clean-enough connection.
And heads were in hands a minute before the interval when a lung-busting run from Perkins saw him produce a superb cross towards the far post.
However, despite busting a gut to get there, Grigg was inches away from tapping in from a yard.
There was still time for Colclough to take a theatrical tumble in the box, which produced neither a spot-kick nor a yellow card for simulation from the referee.
That was Colclough’s last involvement, with the ex-Crewe man giving way to McAleny for the second period.
Haris Vuckic - the hero of last weekend’s narrow win over Bradford - replaced Pearce shortly after the restart, underlining Wigan’s desperation to push forward and win the game.
Lovely play from the Slovenian played in Power, whose low shot forced a great save from Lillis.
The home crowd were treated to a pantomime moment on the hour mark with the arrival off the Dale bench of former Latic Grant Holt.
Holt was given a similarly warm reception when the game got back under way, being immediately clattered - fairly - by Perkins.
That brought cheers from the home fans, who were on their feet again within five minutes as their side finally broke the deadlock.
It won’t win the ‘Goal of the Season’ award, but McAleny’s scrappy effort, after Wildschut had twice been denied, could be as important as any other goal scored this term.
Rochdale threw on Joe Bunney - a headline-writer’s dream at Easter - and the new man was instantly in the play, appearing to be pulled back in the area by Morsy.
Dale were awarded only a corner, which was headed just over by Holt.
Chris McCann took over from Morsy for the last 15 minutes, with the home side trying to push for a second goal while also remaining tight at the back.
McAleny found himself clean through only to again be denied by Lillis, with Vuckic’s smashing the follow-up against the arm of a defender which led to only a corner.
There was almost a twist right at the death when, from another Dale corner, Wabara was required to head off the line, with Holt’s follow-up shot being blocked by Morgan.
But the cheers at the final whistle underlined exactly how important this win could turn out to be come May 8.