Three goals in the second half saw Cavan power back from five points down to claim a seven-point win in the first round of the All-Ireland qualifiers.
Gearoid McKiernan, Niall McDermott and Eugene Keating all netted to send Peter Canavan's Erne men packing.
Fermanagh led by 0-8 to 0-5 at half-time and that stretched to 0-12 to 0-7 when Daniel Kille landed his seventh point of the afternoon.
But the game swung suddenly as Cavan's goals came in an eight-minute spell.
McKiernan finished a good move with a ground shot past Ronan Gallagher in the 17th minute of the second period.
Barely a minute had passed as McDermott was left free for his goal which edged Cavan ahead, 2-8 to 0-13.
Then Keating cut in from the left to blast in after 24 minutes to make it safe for Terry Hyland's side.
All-Ireland qualifiers first round - results
London 2-09 2-11 Antrim
Wicklow 1-17 0-15 Waterford
Westmeath 1-15 0-12 Louth
Tipperary 1-12 0-10 Offaly
Laois 1-10 0-09 Carlow
Longford 0-17 2-08 Derry
Fermanagh 0-15 3-13 Cavan
Roscommon 1-11 1-09 Armagh