Saint Mary's took the lead on a 3-pointer by Stephen Holt with :23 left in the back-and-forth game.
Brownridge scored the Broncos final 10 points and hit baskets to give Santa Clara the lead three different times in the final 3:34 and connected on a pair of 3-pointers in the final two minutes.
Brownridge finished with 23 points to lead Santa Clara (10-8, 3-2 WCC), connecting on 10 of 16 shots from the field and 3 of 4 from long range. Brandon Clark added 20 points for the Broncos.
Brad Waldow scored 17 points, grabbed 14 rebounds and blocked five shots to lead Saint Mary's (13-4, 2-2). Beau Levesque and James Walker III each contributed another 12 points.