Down stung Cavan with a late salvo to edge a scrappy quarter-final tie at a wintry Breffni Park on Saturday.
In predictably testing conditions, the Mournemen goaled on the hour mark and added three unanswered points in the four minutes of injury-time to seal the deal.
Cavan trailed by 0-4 to 0-5 at the interval. Down attacker Cathal Gorman continued to puncture Cavan's hopes after the restart but the hosts worked feverishly against the elements and Paddy Lynch's free (57) levelled matters (0-8 apiece) for the sixth time.
However, determined Down saved their best wine until last and after great work by galloping midfielder Ryan McEvoy, Eoghan Byrne notched a peach of a point to regain the lead.
Cavan desperately tried to spring a get-out-of-jail card but seconds into injury-time, Down hit the jackpot.
A brilliant turnover saw a four-man move end with a palmed goal by sub Conal McNulty.
SCORERS - Down: C Gorman (f) 0-5; C McNulty 1-0; D Rice 0-2; C O'Rawe, E Byrne, R McCormack, S Johnston 0-1 each. Cavan: C O'Reilly 0-3; T Smith, P Lynch (2f) 0-2 each; E Boylan (f) 0-1.
Down - J Hazard; C Fitzsimons, L Toal, J O'Hagan; P Brooks, B Campbell, T Fettes; C O'Rawe, R McEvoy; R McCormack, T Prenter, C Gorman; D Rice, R O'Hare, S Johnston. Subs: E Byrne for D Rice (51); C McNulty for C O'Rawe (25); R Connolly for T Prenter (58).
Cavan - A Smith; D Keappock, P Smith, K Brady; P Nulty, B Smith, E Finnegan; C Donoghue, G Mannion; B Boylan, O Brady, C O'Reilly; E Boylan, P Lynch, T Smith. Subs: T Madden for D Keappock (18); C Boylan for E Finnegan (h-t); R O'Reilly for B Boylan (42); D McGurren for E Boylan (47); E Maguire for T Smith (62).
Ref - K Eannetta (Tyrone).