Aaron Dobbs scored twice as Longford Town staged a second half revival to win this midlands derby and set up a trip to Bohemians in the second round of the Extra.ie FAI Cup.
With six changes from the side that beat Athlone 5-1 in the league just 11 days ago, promotion-chasing Longford duly found themselves on the back foot early on.
Experienced Athlone midfielder Kealan Dillon forced a tip over save from Lee Steacy on six minutes with Jamie Hamilton's resultant corner headed narrowly wide by Nika Kalandarishvili.
Ten minutes later, Hamilton worked a one-time with Georgian striker Kalandarishvili to curl a left-foot shot just over the top as Athlone continued to trouble the home defence.
An out-of-sorts Longford didn’t seriously threaten until the 35th minute when Adam Evans’ goal-bound shot was bravely blocked by Rhys Gorman.
But Neale Fenn's side continued to cough up chances at the other end, the skilful Kalandarishvili dipping a volley just over the crossbar from skipper Aaron Brilly’s cross before Athlone deservedly took the lead on 40 minutes.
Hamilton’s ball in from the left was nodded down by Kalandarishvili for former Longford schemer Dillon to drive his shot past Steacy from 14 yards.
Fenn’s words to his side at half-time clearly had the desired effect as they were level within 38 seconds of the restart.
Athlone lost possession from the tip-off with Joe Manley and Carlton Ubaezuonu then combining to find striker Dobbs in the area to sweep the ball home from close range.
Athlone keeper Aaron Myles was then almost caught out by Ubaezuonu’s chip on 62 minutes, having to backpedal to tip it over his crossbar.
After a bizarre three-minute delay to replace a broken corner flag, Longford went in front on 71 minutes from a corner on the opposite side.
Adam Evans’ delivery bounced all the way through to the back post where Manley was presented with a simple tap-in.
Steacy was required to make the save of the game to prevent Athlone equalising on 77 minutes, reacting instinctively to push away Ciaran Grogan’s close-range header from a Dillon corner.
Grogan, pushed up front, had another chance three minutes from time, but shot straight at Steacy.
Longford then added their third goal in a 92nd minute counterattack, substitute Dean Byrne putting Dobbs through to round Myles and slide the ball home.
Longford Town: Lee Steacy; Joe Manley, Mick McDonnell, Tristan Noack-Hofmann; Karl Chambers, Dylan Grimes, Aodh Dervin, Sean Zambra, Adam Evans (Sam Verdon 72); Aaron Dobbs, Carlton Ubaezuonu (Dean Byrne, 81).
Athlone Town: Aaron Myles; Sean Fitzgerald, Ciaran Grogan, Paddy Kelly, Dean O’Shea; Aaron Brilly (Jabi Amour 79), Jamie Hamilton, Kealan Dillon, Shane Dunne, Rhys Gorman; Nika Kaladarishvili (Ollie Hamzat, 88).
Referee: Eoghan O’Shea (Tipperary).