Tri-Unity led after one quarter 13-10, the score was tied 27-27 at halftime, and Muskegon Heights led 45-41 after three.
The game was tied 53-53 with 1:47 remaining, then Tri-Unity hit a triple and made its free throws down the stretch to seal the victory and move on to the quarterfinals. Tri-Unity outscored the Tigers 21-8 in the fourth quarter.
The loss ended an 11-game winning streak for Muskegon Heights. The Tigers finished with a 14-8 record on the season, after starting out 0-6.
Muskegon Heights won the Lakes 8 Conference championship and a Division 4 district title.
Leading the Tigers was Kevon Washington and Lamonte Townsend with 16 points apiece. Ernest Helms grabbed 10 rebounds in the game.
Brady Titus scored 20 points for Tri-Unity.