Rockford led 22-20 at halftime and 35-29 after three quarters, but Grand Haven dug out the victory with a 20-11 advantage in the fourth.
Ally Keyser had 12 points and six assists for Grand Haven, Kelly Olthof scored nine points and Esther Byington contributed nine rebounds and four blocks.
Grand Haven is now 16-3 overall and finished 9-3 in O-K Red play. The Bucs are currently tied with Rockford for second place in the conference, but Rockford still has a game to play. East Kentwood won the O-K Red with a 10-2 record.