Indiana State (21-9, 12-16 Missouri Valley) had a chance to win, but Jake Odum's 3-point try at the buzzer missed.
The win guarantees Northern Iowa (16-14, 10-8) the No. 3 seed in the MVC Tournament and gives coach Ben Jacobson his 166th victory, tying him with O.M. ''Hon'' Nordly (1938-43 and 1946-54) for all-time UNI wins.
Nate Buss scored 14 and grabbed 11 rebounds for the Panthers and Deon Mitchell scored 10.
Northern Iowa had a 27-17 first-half lead, but Indiana State rallied to lead 39-35 at halftime. The Sycamores' 11-point second-half lead fizzled and Tuttle's 3 at 3:37 put Northern Iowa up 70-67.