Ballymena eased some of the pressure on their manager Roy Walker by securing only their second home league win of the season at the Showgrounds.
Conor Downey played Gary McCutcheon through to score his 22nd goal of the season as the striker slotted past Robert Robinson in the 34th minute.
Aaron Boyd scored the second from an Alan Teggart cross after 43 minutes.
Jordan Baker was wide with a second-half effort and Teggart went close as Ballymena move up to seventh place.
McCutcheon shot well over early in the game and then Ryan Henderson's flicked header was tipped over by Wayne Drummond.
Donegal Celtic were disappointing and they swap places with their opponents in the Premiership standings.