Mitchell was 8 of 11 from the field with 27 points. Tuttle was 6 of 9 from the field, with 21 points. He also had a team-high 10 rebounds. Marc Sonnen added 11 points for the Panthers (2-0).
Northern Iowa had a 41-38 lead at halftime, but Toledo was not done.
At the end of regulation, the score was tied at 70. Northern Iowa scored 14 points in overtime.
The game was the first-ever meeting between Northern Iowa and Toledo in basketball.
Toledo is a favorite to win the Mid-American Conference's West Division.