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.
Leaving early for the NBA is a risky decision. Some players -- Skal Labissiere, Dejounte Murray -- slid in the draft. Some -- Isaiah Taylor, Troy Williams -- weren't drafted at all.
College basketball coaches across the country will hit the recruiting trail hard in July to target the Class of 2017's top prospects. Which players are the nation's top programs targeting?
The Tar Heels could lose Justin Jackson and Kennedy Meeks after next season. Coach Roy Williams has nearly every top-10 2017 prospect on his board.