The Rockets managed just seven points in the first half, but they only trailed 14-7 at halftime due to solid defensive play.
The Rockets came to life in the third quarter, outscoring the Bucs 13-3 and taking a 20-7 lead in the fourth.
The game remained close down the stretch. Jazmin Wright-Zornes sealed the game for the Rockets by hitting two clutch free-throws with 11 seconds left to extend the lead to five.
Brooke Larabee scored 15 points and grabbed 11 rebounds for Reeths- Delaney Bolles Puffer while added 11 points.
Alli Keyser scored 12 points for Grand Haven, which finished the season with a 10-12 record. Alexia Bouwhuis chipped in 10 points.
The Rockets advance to the district championship game on Friday, when they will meet Mona Shores. The teams played twice in the regular season, with the Sailors winning both contests.