Four points separated the sides at the break (0-9 to 0-5) before the hosts went on a scoring rampage on the restart to ease to victory.
Ryan Bogue and Sean Corrigan were the scorers in chief for the Ulster men in that opening spell while all of Longford’s scores came from midfielder Eoin Donnellan.
But Fermanagh took charge after the break with a John Paul McGarry goal the catalyst for the scoring onslaught. Donnellan kept his side in touch from placed balls but it was merely a case of damage limitations for the visitors.
Bogue hit five points in succession to end the rout and book a semi-final spot later next month.
FERMANAGH: McPhillips; Mahon; Bannon; Mulholland; McBrien; Slevin; Kehoe; Goldrick (0-1); Bogue 0-9 (7f, 1 65’); Duffy (0-2); Morrissey; J P McGarry (1-1); Corrigan (0-5); D McGarry; Breslin (0-1).
Subs: McManus for Goldrick; Timoney for Breslin; Curran for Morrissey; Porteous for Bannon.
LONGFORD: O’ Reagan; Connolly; Browne; Carroll; Kavanagh; Finucane; Hegarty; R Donnellan; E Donnellan (1-8, 9f); Breslin; Newman; Murray; C Corcaran; Daly; P Corcoran.
Subs: Molihan for Kavanagh; Roche for Breslin; Kelly for C Corcoran; McGarry for Murray.
Referee: Brendan Sweeney.