After Treadwell went to the bench, Harney and Diggs combined to score 12 points to push Akron's lead to 71-58 with 3:16 left.
Joshua Freelove scored 17 points for Buffalo (18-9, 12-5) and made four of the Bulls' seven second-half 3-pointers. The loss snapped a four-game winning streak.
Akron avenged a 96-90 loss at Buffalo on Feb. 19.
Ohio beat Bowling Green 72-61 on Tuesday, preventing Akron from locking up a bye (No. 4 seed) in next week's tournament.