Longford will play Division 4 football next season following a lacklustre affair at Páirc Esler in Newry where the hosts Down pulled away in the finish to win by five points.
A combination of Liam Kerr's 67th-minute penalty and Pat Havern’s three second-half points were enough to relegate this season's O’Byrne Cup winners with a round to spare.
Paddy Christie’s side whimpered down a division and will play in the bottom rung of the Allianz League for the first time since 2015 with the visitors ending the game with 14 men after Joe Hagan received his marching orders with five minutes to play.
With results elsewhere impacting Down’s promotion chances long before throw-in, the hosts laboured into the contest along with a doomed Longford.
Mourne wing-forward Liam Kerr took the smaller than usual crowd out of its slumber with an early free. Then unfortunately, Mark Walsh suffered a serious injury and had to be stretchered off with the utmost of caution after a long delay.
With the game restarting in effect, Longford took their chance at the second time of asking. Dessie Reynolds and Dylan Farrell shooting them into an unlikely lead.
One of eight Kilcoo men on the panel, Ryan Johnston burst through from right half-back to level the game.
Midway through the half neither side could separate themselves from each other. In fact, they would find themselves tied on three more occasions. Michael Ireland and Pat Havern gave Down the slight advantage but Michael Quinn and Oran Kenny duly pulled the sides back to parity.
Mourne manager Conor Laverty was forced to play full-forward Havern in the middle of the field, and he revelled in the open space especially when shooting from long range.
That Havern injection along with the excellent Míceal Rooney quickly pushed Down into a healthy lead, 0-07 to 0-04.Then, with the lengthy injury time called out on the tannoy, Darren Gallagher pointed, and with his next attempt going short, Dessie Reynolds flicked home.
Despite that major, Kerr and Rooney pulled points back and just when it looked like the home side would edge the half, Daniel Mimnagh made it 1-06 to 0-09 at half time.
Bar an interval replacement in goals for Down, Niall Kane replacing Charlie Smyth, the second half continued in much the same vein.
Liam Kerr sandwiched scores from Longford's Jack Macken and Dylan Farrell and the half plodded along.
With his eye well and truly in, Havern was pushed closer to goal he landed three of the next four scores and that provided Down with the impetus to control the outcome.
With the home side baying for blood, they were unlucky and found Longford tough to pass through for goal. That eventually resulted in the decisive penalty where Joe Hagan picked up a black card and then red.
The lively Kerr dusted himself down after the foul to secure the points and finish off Longford’s hopes of survival.
Down: Charlie Smyth; Peter Fegan, Ryan McEvoy, Finn McElroy, Ryan Johnston (0-02), Pierce Laverty, Conor Fitzpatrick; Pat Havern (0-05, 0-02fs), Mark Walsh; Miceál Rooney (0-02), Donagh McAleenan, Liam Kerr (1-05, 1-00pen, 0-03fs); Jerome Johnston (0-01), Michael Ireland (0-01), Conor McCrickard (0-01).
Subs: Tom Close for Walsh (13), Niall Kane (0-01, 0-01 '45) for Smyth (ht), Rory Mason for McCrickard (40), Eamon Brown (0-01) for Ireland (40), Conor Francis for J Johnston (54).
Longford: Paddy Collum; Barry O’Farrell, Andrew Farrell, Patrick Fox; Iarla O’Sullivan, Michael Quinn (0-01), Ryan Moffett; Jack Macken (0-01), Darren Gallagher (0-01); Dylan Farrell (0-05, 0-03fs), Daniel Mimnagh (0-01), Joe Hagan; Rian Brady, Dessie Reynolds (1-01), Oran Kenny (0-01).
Subs: Aaron Farrell for R Brady (40), Peter Foy for O’Farrell (46), Keelin McGann (0-01) for Kenny (46), D O’Brien (0-01) for Reynolds (60), F Sheridan (0-01) for Macken (68).
Referee: S Laverty (Antrim).