Crusaders retain their fourth position in the Premiership thanks to two second-half goals at Seaview.
In the first half, Celtic's Ciaran Gargan clipped the bar with a free-kick and a Gary McCutcheon free-kick fizzed over the bar for the Crues.
Chris Morrow flashed a shot wide and David McMaster saw his strike saved.
Morrow gave the Crues the lead with a glancing header from a right-wing cross on 75 minutes and McCutcheon made it 2-0 from the penalty spot on 80 minutes.
The former Portadown and Ballymena United forward stepped up to score after being pulled down in the area by Sean Cleary.
Cleary had an attempt saved by Sean O'Neill in the first half.
Donegal Celtic are still looking for their first league win of the season and remain 11th in the Irish Premiership table, level on points with basement side Lisburn Distillery.