Mitola, who finished with 18 points, grabbed the lead for Dartmouth (5-5) twice in overtime with 3-pointers before Jordan Threloff hit two free throws and Aaric Armstead made a layup for the Huskies (4-4) for a 55-52 lead with 1:26 left.
Mitola's third trey of the period tied it at 55 with 45 seconds left. A missed layup by Michael Orris set up Mitola's winning 3. Mitola had all 12 of Dartmouth's points in overtime.
Armstead paced Northern Illinois with 12 points and eight boards. He hit a tying 3-pointer to force overtime after the Huskies erased a double-digit deficit in the second half.