Monday, the Pilots (17-14) will play Saturday's BYU-Santa Clara winner.
Portland came into the tournament on a four-game losing streak. The Gaels (21-9) had beaten Portland nine consecutive times and had won all four meetings between the teams in previous WCC tournament games. Randy Bennett had coached the Gaels to the WCC semifinals in each of his previous 13 seasons at Saint Mary's.
Portland never trailed and, leading by six, outscored the Gaels 18-7 over the final 6:36, including eight points from Bailey and seven from Todd.
Thomas van der Mars and D'Marques Tyson each scored 10 points for Portland, which hit half of its 46 shots.
Brad Waldow scored 25 points and had eight rebounds for the Gaels, who shot just 30.2 percent.