The Buccaneers had built a 4-2 lead behind goals from Asa Pellegrom, Will Verduin, Austin Way and James Dyksterhouse.
The Forest Hills team fought back as Sam Renneker scored back-to-back goals to tie the score, then Brad Reitter put the game-winner in the net.
The Bucs fall to 10-3 overall and 4-2 in O-K Tier II action.
Zach Kooi made 16 saves for the Bucs while Bryce Bignall had 23 stops for Forest Hills.
Tom Zelenka, Ian Hibbard and Dyksterhouse provided assists for Grand Haven, which returns to action on Friday against Grand Rapids Catholic Central. The puck drops on that contest at 7:30 p.m. at the Grand Rapids Edge Ice Arena.