Playing in a new role, at centre-forward, McGlynn showed superb awareness and precision, when he took a pass from Odhrán Mac Niallais, before spinning onto his left foot to sail his shot over goalkeeper, Stephen Kane.
Rory Gallagher’s experimental team saw debutant, Ciaran Thompson, kick three points, while Michael Murphy marked his 100th game for the county with a score, after coming on as a sub in the second half.
Donegal could have won by more, had the newcomers, Eoghan Ban Gallagher and Jack O’Brien, found the net.
Gallagher drilled wide, after taking receipt of a clever palm-down by Leo McLoone, while corner-back, O’Brien, cracked a powerful shot off the Down crossbar.
Murphy also looked destined for a goal, in the closing stages, but lost his footing at the vital moment.
Donegal reeled off a succession of points in the third quarter, including one from defender, Paddy McGrath, that was his first score in his 63rd appearance.
New Down boss, Eamonn Burns, was left to curse eleven wides, although Down were in the game until the end, as Donegal couldn’t quite pull away.
Donegal gave a late cameo to St Eunan’s forward, Cillian Morrison, who has decided to concentrate on Gaelic football, having played League of Ireland soccer with UCD and Derry City in recent years.
Morrison, a member of the Donegal U21 squad in 2010, had played for St Eunan’s in their Ulster club campaign, last year, and has been in training with the county squad in recent weeks.
D Rodgers; J O’Brien, E Doherty, P McGrath (0-1); E Gallagher, M O’Reilly (0-2, 2f), C Ward (0-1); H McFadden (0-1), C Thompson (0-3); M Carroll, F McGlynn (1-1), S McBrearty; O Mac Niallais (0-1), L McLoone, E McHugh.
M Murphy (0-1) for Carroll (52), C Morrison for McHugh (69).
S Kane; M McGee, C McGovern, R Boyle (0-1); R Mallon (0-1), A Carr, D O’Hanlon (0-2, 2f); P Turley (0-1), C Doyle (0-1); J McDermott, C Mooney, J Murphy; G Johnston (0-2), A McConville (0-1, 1f), S Dornan (0-1).
D Turley for McDermott (45), B O’Hagan (0-1) for Murphy (59), M McKay for McConville (59), C Harrison for Dornan (59), P Downey for P.Turley (66).
M McNally (Monaghan).