Sheriff were on the back foot from the start with Peter Halpin having to make a smart save with his feet inside four minutes to thwart David O’Sullivan, who’d been put through onto strike-partner Gary Shaw.
Halpin was busy again within nine minutes, doing well to parry from O’Sullivan’s shot on the turn as Longford started brightly.
Stephen Rice shot wide from Lorcan Shannon’s corner while Kevin O’Connor shaved the bar with another long-range effort before dominant Longford got their deserved lead on 25 minutes.
O’Connor and Shaw produced some clever footwork inside the area, before the latter set up O’Sullivan to shoot home from 15 yards.
Though they had a goal disallowed for an infringement, Sheriff had scarcely been in the game before levelling with a sublime strike in first half stoppage time. With nothing seemingly on, midfielder Joseph Flood looked up and dipped a 30-yard shot over Longford keeper Paul Hunt for a spectacular goal.
But two goals inside as many minutes from the start of the second half all but ended the game as a contest.
Ayman Ben Mohamed restored Longford’s lead less than a minute after the restart, racing through to drill a low shot to the corner of Halpin’s net.
Less than two minutes later, Longford got a third. The impressive O’Connor threaded a terrific ball through for the run of Shannon who did well to place his shot from the edge of the area into the corner of the net.
Sheriff battled hard late on, and had a second goal disallowed, before substitute Darren O’Brien was sent off on 90 minutes for a second booking.
Longford Town: Hunt; Haverty, Gorman, Rossiter, Powell; Shannon, O’Connor (Salmon 85), Rice, Ben Mohamed (Simon 73); O’Sullivan (Gannon 65), Shaw.
Sheriff YC: Halpin; P. Murphy, Kavanagh, Browne; Lester (O‘Brien 71); Higgins, Joseph Flood (Joyce 81), D. Dunne, Lynch; Rock, Glen (T. Dunne 63).
Referee: Neil Doyle.