Donegal manager Brian McIver almost had his plans for a winning start to his tenure scuppered by his own son at Ballyshannon as the home side survived to escape with a 0-13 to 1-8 win.
McIver's son Michael hit an early goal to help St Mary's into a 1-2 to 0-0 lead in a tightly-contested Dr McKenna Cup Section C tie, but Donegal came good.
The sides went in level at the break - 0-7 to 1-4 - after points from Ciaran Bonner, Brendan McDyre, Colm McFadden, Gavin Maguire and Adrian Sweeney had got McIver's men up and running.
After Sweeney hit a goal chance off the post early in the second half, Bonner also watched agonisingly as St Mary's stopper Martin O'Kane parried his effort away.
Conal Dunne also missed a chance for a major, but despite the influence of Down star Dan Gordon and Tyrone's All-Ireland winner Joe McMahon for the visitors, late points from Maguire and Christy Toye, from a punched effort, handed Donegal victory.
