Also scoring in double figures for top-seeded Gonzaga (27-6) were Gary Bell Jr. and Sam Dower with 14 and 12 points, respectively. Dower also cleared a game-high nine rebounds.
The fourth-seeded Gaels (22-11) were paced by Brad Waldow with 14 points, Stephen Holt 13 and Kerry Carter 11 points.
The Bulldogs scored the first points of the contest, shooting a modest 45.5 percent from the field in the first half and adding an 8-of-8 performance at the free-throw line to claim a 31-20 advantage.
SMC knocked down nine field goals and missed all their shots behind the 3-point line through the first 20 minutes.
Gonzaga hit 46.4 percent from the floor in the second half, but only 11-of-18 at the charity stripe.
Saint Mary's finished with almost as many turnovers (17) as field goals (19) and converted a meager 14-of-25 at the free-throw line.
With the victory, Gonzaga advances to the title game against BYU, which defeated San Francisco on Monday.