Three injury-time points helped Louth account for hosts Armagh on a 1-12 to 1-10 scoreline in this Allianz NFL Division 2 clash at the Athletic Grounds.
Brian White, who missed an earlier penalty, hit an equalising free before Ciaran Byrne and Shane Lennon pointed the Wee County to a precious away win.
Both teams lost a player in the second half with James Donnelly and Gerard Hoey seeing red. Adrian Reid and Tony Kernan scored goals within three minutes of each other in the first half.
Armagh actually finished the game with 13 men when James Lavery hobbled off two minutes from the end, having already used all five substitutes.
Aidan O'Rourke was facing his native Armagh for the first time since taking over as Louth manager. The teams were level nine times in this local derby before Louth stepped up to steal the points.
The visitors suffered a pre-match blow when Paddy Keenan failed a late fitness test. Armagh were without the injured Aaron Kernan and Ciaran McKeever plus Jamie Clarke who is away on holiday.
Both sides seemed to miss their absent players and were slow to settle. The first 20 minutes were extremely scrappy with poor distribution and misplaced passes the main feature of the play.
They were level three times in the opening quarter. Derek Crilly's 20th-minute point put Louth ahead after Adrian Reid, Shane Lennon and Brian Donnelly had already scored from play for the Wee County.
Armagh wasted a lot of chances early on and hit six wides in the first half. They also hit the post and defender James Donnelly cracked a shot off the crossbar in the 13th minute when he looked certain to bust the net.
Louth made Armagh pay for their wastefulness when Adrian Reid drilled home the opening goal after 23 minutes. Ronan Carroll's pass took out a couple of defenders and Reid's low shot deflected off Philip McEvoy and into the net.
Andy McDonnell made sure with the final touch but the ball already looked to have crossed the line to put Louth 1-04 to 0-03 ahead.
Armagh responded with a goal from Tony Kernan three minutes later. Declan McKenna, who was finding a lot of room running through the middle of Louth's defence, lobbed the ball out to the unmarked Kernan who dummied goalkeeper Neil Gallagher and tapped the ball into an empty net.
Points from Gavin McParland and Caolan Rafferty, plus a superbly struck '45' from Brian White, saw the sides go in level at 1-05 apiece at the break.
Darren Clarke, often so influential for Louth, had a quiet night and was replaced early in the second half at a stage when the visitors struggled for scores.
Clarke's replacement, Derek Maguire, scored a spectacular point within a minute of coming on. Armagh were reduced to 14 men after 46 minutes when James Donnelly was sent off for a second yellow card - a foul on Kevin Rogers - when the sides were level at 1-06 each.
The home side responded by opening up a two-point lead with scores from Stephen Harold and Stefan Forker, before the latter was surprisingly taken off.
In keeping with the pattern of the game, Louth hit back with two points to level it up at 1-09 apiece after 53 minutes. Brian White missed a penalty for Louth seven minutes from the end, and that proved to be a crucial miss.
White went for power but his shot was well wide of the keeper's right hand post, but he showed great character to land the equalising free which put Louth on the road to victory.
ARMAGH: P McEvoy; J Morgan, B Donaghy, J Donnelly; F Moriarty, D McKenna (0-01), A Duffy; J Lavery, S Harold (0-02); C Rafferty (0-01), J Hanratty, S Campbell (0-01); T Kernan (1-00), S Forker (0-02, 0-01f), G McParland (0-03, 0-02f).
Subs used: M Shields for Morgan (31 mins), B Loughran for Duffy (46), B Mallon for Forker (49), K Toner for Hanratty (58), S Clarke for Campbell (64).
LOUTH: N Gallagher; C McGuinness, D Finnegan, G Hoey; P Rath, D Crilly (0-01), A Reid (1-01); R Carroll, B Donnelly (0-01); A McDonnell, M Brennan, B White (0-02, 0-01f); D Clarke, S Lennon (0-03), K Rogers (0-02, 0-01f).
Subs used: D Maguire (0-01) for Clarke (41 mins), J McEneaney for McGuinness (51), C Byrne (0-01) for Rogers (61)
Referee: Eddie Kinsella (Laois).