The game was close from start to finish.
The Spartans led 30-25 at halftime and 44-39 after three quarters, then held off the Wildcats down the stretch.
Ryan Mount led the Spartans with 18 points while Austin Tyndall added 11.
Montague was pace by Jacob Buchberger with 19 points.
Mason County will play Shelby on Friday night at Montague for the Class C district championship at 6 p.m.