Donegal, cheered on by a crowd of over 6,000, got their first brace of league points thanks to a commanding second-half performance in Ballybofey.
In perfect conditions, on a night borrowed from the summer, Down led by three points with minutes left to half-time but two late frees from Michael Murphy and Colm McFadden left just a point between them at the break, 0-5 to 0-4.
The introduction of Neil Gallagher for his 100th game for the county saw a resurgent Donegal after the break as Down were held scoreless until the 65th minute.
The home side had built up a six-point lead by that stage, 0-11 to 0-5, with Murphy and Rory Kavanagh keeping Down on the back foot.
It was Murphy's fourth game in 11 days and his tally of 0-29 in that period underlines his importance to DCU and Donegal.
He was ably assisted by Mark McGee, Mark McHugh, Rory Kavanagh, Anthony Thompson and Eamon McGee, who was central to Donegal staying in the contest when Down were threatening in the opening half.
There were other positives for Jim McGuinness with another member of the McHugh clan, 18-year-old Ryan, making an impressive debut, while Ross Wherity flourished when moved further outfield.
Down had a big call for a penalty as Donal O'Hare broke clear on 51 minutes with Neil McGee clearing off the line, but with just two scorers on the night, they cannot have any complaints with the final outcome.
Donegal manager McGuinness said afterwards: "The big bonus from tonight was Ryan McHugh, who was a minor last year, coming into the team.
"The longer the game went on, the more he settled into it.
"The same goes for Ross Wherity. I've said this all along, you want to use the league as a vehicle to try to unearth a player or two and also to look at different things in terms of how you play the game.
"We did both of those things tonight and it was pleasing and to get the points on top of that.
"Some days you do that and don't get the points, but you're still building towards the summer," he said.
Next up for Donegal is the clash with Tyrone in Omagh, and with the sides also meeting in the first round of the Ulster championship, this outing will have considerable interest.
McGuinness, however, played it down. "It's the same thing. We want to look at players. We want to try things out. We want to win the match, so there's no difference at all."
Man of the Match: Eamon McGee (Donegal)
Scorers - Donegal: M Murphy 0-6 (4f), D Walsh, L McLoone, R Kavanagh, C McFadden (f), R Wherity and D McLaughlin 0-1 each. Down: D O'Hare 0-5 (4f), K McKernan 0-2 (1f).
Donegal – P Durcan 6; D Walsh 7, E McGee 9, N McGee 8; R McHugh 7, A Thompson 7, M McHugh 7; R Kavanagh 7, M McElhinney 5; R Wherity 7, L McLoone 5, R Bradley 7; P McBrearty 5, M Murphy 8, C McFadden 6. Subs: N Gallagher 7 for McElhinney (h-t); D Molloy 5 for McBrearty (55); D McLaughlin 6 for McFadden (63); O Mac Niallais 5 for N McGee (70).
Down – M Cunningham 8; D Turley 7, D McCartan 7, R Boyle 5; R Mallon 6, A Carr 6, B McArdle 5; K King 5, K McKernan 8; K Quinn 5, M Poland 7, P McComiskey 5; C Laverty 6, C Harrison 5, D O'Hare 8. Subs: P Turley 5 for B McArdle (h-t); B Coulter 5 for Harrison (47); D Rooney 5 for Mallon (48); D Savage 5 for D Turley (56); C Gough 5 for King (58).
Ref – M Duffy (Sligo)