The Vikings defeated a ranked team for only the second time in school history. The other such victory came in the 1986 NCAA Tournament against Indiana.
Cleveland State (13-5, 6-0 Horizon) has opened conference play with six consecutive wins for the first time in 15 years.
Butler had an eight-game winning streak snapped.
Bullock put Cleveland State in front for good at 48-46 with 4:54 remaining and Jackson made a key three-pointer for a 53-48 advantage.