Declan Byrne's late point rescued a draw for Louth at Pearse Park, but it wasn't enough to deny Longford a semi-final date with Westmeath.
Longford, who are without the services of the Mullinalaghta players, started with only five of last year's championship team, but that didn't worry new manager Padraic Davis.
"This is the perfect opportunity for the younger players and some of them gave a great account of themselves," he said.
"Overall, we are happy with the direction we are going. I think the most pleasing thing about this game was the way our lads responded when Louth upped the tempo in the second half. Peter Lynn put in a terrific shift.
"It's great to see all the young lads - including Darren Doherty - doing so well. We can't ask for much more than what they are giving."
ScoreRs - Longford: R Smyth 0-6 (4fs), D Gallagher 0-4 (3fs) P Lynn 1-1, D Doherty 0-2, S Donohue, P Gill, C P Smyth 0-1 each.
Louth: T McEneaney 1-2, D Byrne 0-4, S Mulroy 0-3 (3fs), Downey 0-2, A Williams, R Holcroft, C McKeever, R Nally, J McEneaney 0-1 each.
Longford - P Collum; P Lynn, B O'Farrell, S Donohoe; D Quinn, A Farrell, D Gallagher; C Shields, P Hanley; M Quinn, C P Smyth, P Gill; B McKeon, R Smyth, D Doherty. Subs: PJ Masterson for C Shields (57), L Connerton for Gill (57), C Lee for Farrell (62).
Louth - A McGauley; F Donohue, D Marks, J Craven; L Grey, A Williams, E Callaghan; B Duffy, T Durmin; C Downey, R Holcroft, D Byrne; N Conlon, S Mulroy, T McEneaney. Subs: J Clutterbuck for Grey (17), C Earley for Callaghan (h-t), D Corcoran for Donohue (h-t), C McKeever for Conlon (h-t), C Brannigan for McEneaney (h-t), J McEneaney for Holcroft (44), E Duffy for Downey (59), R Nally for Mulroy (62).
Ref - F Smyth (Offaly).