Hahn made a pair of free throws with 7 seconds left to give Butler a three-point lead. Loyola could only manage a free throw by Courtney Stanley with 3 seconds left.
Butler (4-2), the four-time defending Horizon champion who was the national runner-up last season, led 38-28 at halftime before the Ramblers (7-1) rallied, but Loyola never drew even. Shawn Vanzant's 3-pointer with 3 minutes left gave the Bulldogs a 63-56 lead.
The Ramblers are off to their best start since 1962-63, when they began 21-0 and ended the season with the NCAA championship.