With the loss, Saint Mary's drops to 1-2-1 while UC Riverside improves to 2-2-0.
UC Riverside held a slim 12-11 shots edge and the Gaels held a shots on goal advantage of 6-5. Saint Mary's attempted nine corner kicks in the game, compared to six by UC Riverside. UCR committed 18 fouls while SMC had 10 fouls.
In a scoreless first half, the Gaels and Highlanders each took four shots and two shots on goal. SMC attempted just two of its nine total corner kicks in the first half.
UCR would score in the 71st minute on a goal from 30 yards out by Cesar Diaz Pizzaro. His shot went into the upper right corner of the net, taking a pass from Aaron Long.
Riley Hanley took two shots on goal to pace the Gaels, while Jose Cabeza and Bobby Conner also took two shots. Conroy Cunningham and Emmanuel Sarabia also fired shots on goal for SMC.
Diaz Pizzaro took a game-high five shots.
Saint Mary's is back in action on Friday when it hosts Sacramento State at 4:00 p.m. in Saint Mary's Stadium.