Two late scores from wing-back Derek Horan and Fennell gave Louth a 0-8 to 0-6 half-time lead. Ronan Byrne and midfielder Shane Callan pushed Louth’s advantage out to three before Fennell scored the first goal. Wallace and Gerard Smyth added points to emphasise Louth superiority.
On 57 minutes, that dominance was rubber-stamped when Dunne scored an eye-catching goal.
Donegal’s Harrigan was sent off on a second yellow and Dunne fired the third goal eight minutes from time. Wallace, Donagh O’Sullivan and a pair of Murphy points rounded off the scoring.
Scorers for Donegal: N Campbell 0-2 (1f), S McVeigh, E McDermott, D Cullen, R McDermott, E Organ 0-1 each.
Scorers for Louth: S Fennell 1-5 (5fs), D Dunne 2-0, D Murphy 0-4 (1f), A Wallace 0-3, Donagh O’Sullivan, R Byrne, D Horan, S Callan, G Smyth (1f), B Corcoran 0-1 each.
DONEGAL: P Burns; B Harrigan, J Boyle, P Doherty; C McDermott, Justin McGee, J Donnolly; S McVeigh, A McDermott; E McDermott, D Cullen, R McDermott; L Henderson, E Organ, N Campbell.
Subs: K Campbell for R McDermott (52), P Sheridan for Boyle (56).
LOUTH: J Connolly; D Rafferty, W Morissey, M Wallace; Donagh O’Sullivan, R Byrne, D Horan; S Callan, D O’Hanrahan; D Dunne, S Fennell, D Murphy; K McNally, B Corcoran, A Wallace.
Subs: G Rellis for O’Hanrahan (40), G Smyth for McNally (63), S Maguire for Fennell (65), D Mahoney for Wallace (67), D McKiernan for Murphy (68).
Referee: O Elliott (Antrim).