On the restart, Rovers survived an early scare close to their own line but when, on his return to action, Rob Purdham flung out a wild pass on 44 minutes Dobson snatched the ball to race 80 metres to claim his second try.
McFadden's 68th-minute free doubled Donegal's lead although the Ulster county had a scare seconds later when goalkeeper Boyle almost dropped a high ball over his own goal-line before Eamon McGee averted the danger.