Ballymena moved into fifth place in the Premiership and to within a point of Crusaders by coming from a goal down to secure victory at the Showgrounds.
Gary McCutcheon scored on 25 minutes after Dwayne Nelson sliced a clearance.
Alan Davidson levelled three minutes later with a classy finish past Sean O'Neill after a slip by Josh Robinson.
James Costello reacted quickly to head home after Davidson's header had been palmed away on 82 and the striker shot wide from 40 yards and hit the post.
Costello and David Cushley had early chances for Ballymena in an entertaining game, while Jordan Owens squandered an opportunity for the Crues.
McCutcheon broke the deadlock against his former team by finding the net for his seventh goal of the season.
Paul Heatley went close on several occasions and Ballymena's Aaron Stewart was off-target with a glancing header.
In the second half, Nelson turned away a Heatley shot, Owens headed just over and Gary Thompson had a chance at the other end for the Sky Blues.
After Costello's winner, Declan Caddell twice missed with headed attempts in front of goal when he should have done better.
Costello, back from injury, showed some of the form which made him Northern Ireland Football Writers' Player of the Month for April last season, when he twice almost found the net again late on.