Dane Massey, David McMillan, and Daryl Horgan provided the goals to leave Dundalk on the cusp of a third successive title on a bittersweet night for their manager Stephen Kenny at City Calling Stadium.
The almost pedestrian victory, in tandem with Cork City losing 3-1 at St Patrick’s Athletic, moves Dundalk seven points clear at the top of the Premier Division.
With three games to play, it means Dundalk will be going for their 12th league championship when Bohemians visit Oriel Park on Sunday night.
And they might not even need to wait that long should Cork slip up again when St Patrick’s visit Turner’s Cross on Friday.
But the night was also tinged with sadness for Kenny, who began his managerial career at Longford, as it’s his side’s win that confirms their relegation back to the First Division after two years up.
Comfortable 4-0 winners on their last visit to the midlands in April, Dundalk’s intent was there from the off with Longford keeper Ryan Coulter off his line promptly inside 30 seconds to save at the feet of McMillan after Patrick MceEleney’s clever hooked through ball.
Two minutes later, Dundalk defender Brian Gartland worked Coulter again with a header into the keeper’s arms from John Mountney’s first corner of the night.
From a second Mountney corner six minutes minutes later Massey should have scored, but planted his free header straight at Coulter on his line.
But Massey has always been a little more assured with his left foot as his next sight of goal emphatically found the target to put Dundalk deservedly in front on 15 minutes.
Alan Keane tenaciously nicked the ball off a Town defender on the edge of the area to lay the ball back.
And left-back Massey took a controlling touch before seeing his low drive from 30-yards arrow to the bottom corner of Coulter’s net to score for the second successive match.
The joy of the lead was soon soured a little as an injury forced Mountney off to add to Stephen O’Donnell and Sean Gannon on the sidelines.
With Darren Meenan on, the pressure on the home goal didn’t relent as Coulter was forced into a smart save on the half hour.
A slip by Town’s Pat Flynn set McMillan away on the left. Horgan collected the pass to turn neatly on the edge of the area to bring a diving save from the keeper.
Struggling to get into the game, Longford finally contrived a goal attempt on 36 minutes, Kealan Dillon’s shot from distance working Gabriel Sava.
Dundalk remained well on top, though, and duly added to their lead four minutes before half-time with a delightful goal. Meenan picked out Ronan Finn in the inside-right channel with the midfielder’s sublimely weighted pass put McMillan through to score with a crisp, angled dive for his 16th of the league season.
McMillan was then involved as Dundalk took just three minutes of the second half to stretch their lead.
The striker turned well to send McEleney away on the left. And though his low cross was out of the reach of Horgan, Longford captain Conor Powell’s attempted clearance struck the Dundalk winger to fly into the net.
Coulter; J. Mulhall, Flynn, Gorman, Powell; Hughes (Makouta, 85), Dillon (Gannon, 62), O’Connor, McGlynn; Cowan (Dsane, 71), O’Sullivan.
Sava; Keane, Gartland, Boyle, Massey; Shields (Benson, 57), Finn; Mountney (Meenan, 21), McEleney, Horgan (Kilduff, 76); McMillan.
James Mckell (Tipperary).