Pressley made 4 of 6 field goals, including 3 of 4 from 3-point range, and 6 of 6 free throws and Portland (8-3) shot 55 percent (32 of 58) overall. Thomas van der Mars added 12 points, D'Marques Tyson scored 11 and Volodymyr Gerun 10.
Montana State (3-8) made just 8 of 22 (36.4 percent) field goals and committed 11 turnovers in the first half and Portland took a 50-29 lead into the break.
Terrell Brown's jumper with 11:29 left in the first half gave Montana State a 16-14 lead, but the Pilots scored 18 of the next 21, opening up a 13-point lead when Pressley hit a 3 about 7 minutes before halftime.
The Bobcats trailed by double digits the rest of the way.
Danny Robison led Montana State with 24 points.