Deilvez Yearby had eight points and 10 rebounds for the Mastodons (16-14), the fifth seed in the tournament. They advance to meet regular-season champion Oakland, Mich., in Monday's semifinals.
Garrett Callahan led fourth-seeded South Dakota State (14-16) with 20 points. Kai Williams had 17 points and eight rebounds for the Jackrabbits.
Neither team led by more than seven points in the game, which was tied 28-28 at halftime. IPFW made 54 percent of its shots in the second half and 49 percent for the game.