The Bruins (26-4, 18-1 Atlantic Sun Conference) used a 13-0 run midway through the second half to lead 58-38. J.J. Mann made a layup with 7:28 left to play, extending the Bruins' lead to 64-40.
Belmont led 39-32 at halftime despite Mercer's 50-percent shooting effort in the opening half (11 of 22).
The Bears (13-17, 10-9) ended the game on a 24-11 run, but their 15 turnovers and poor second-half shooting (12 of 32, 37.5 percent) were too much to overcome.
Brian Mills scored 15 points and grabbed eight rebounds for Mercer, which was outscored 36-22 in the paint and 40-29 in bench points.
Belmont has won eight straight and 17 of 18, while remaining a perfect 21-0 against teams from outside the state of Tennessee.