Eric McClellan added 19 points and Domantas Sabonis had a career-high 20 rebounds and 12 points for the Bulldogs (15-5, 7-2 West Coast), who broke the game open with a late 13-2 run.
Kyle Dranginis started the winning run with a 3-pointer at the 6:14 mark to put Gonzaga up 52-48. Wiltjer scored the next eight, sandwiching a tip-in between a pair of 3s. After a jumper by Alec Kobre, who led the Tigers (6-13, 3-5) with 20 points, the Bulldogs made four free throws to lead 64-50 with 2:43 remaining.
Gonzaga, which led 26-25 at the half, shot 52 percent (12 of 23) and made 17 of 25 free throws in the second half when McClellan and Wiltjer combined for 29 points.
Pacific led 40-35 with 14:48 to play after back-to-back 3s from David Taylor and Ray Bowles.