Guercy's 3-pointer put the Owls (5-11, 2-3) up 69-66 and Marcus Jackson added two free throws 10 seconds later. Braxton Ogbueze scored for the 49ers (8-9, 2-3) before Guercy, who finished with seven points, added two final free throws with 13 seconds left.
Rice's Seth Gearhart scored the final six points of regulation to tie the game at 59-all.
Jackson led the Owls for the fifth straight game with 20 points. Gearhart scored 18, all but two in the second half, and Mency added 13 and Andrew Drone 10 for Rice, which broke a three-game losing streak.