Saint Mary's trailed early before taking the lead for good at 7-5 on Hermanson's 3-pointer - near the start of a 19-4 run. Adom Jacko's dunk late in the half pulled the Lions within five, but the Gaels scored the last seven of the half and went unchallenged through the second.
Jacko had 21 points on 9-of-11 shooting and grabbed eight rebounds for Loyola Marymount (7-8, 0-4).
The Gaels, at 25-of-52 shooting, were slightly under their nationally top-ranked field-goal percentage (54.3 percent) entering the contest.
Saint Mary's and Gonzaga are the conference's remaining unbeaten teams. The Gaels host the Bulldogs on Jan. 21.