The Vikings (8-11, 3-5 Big Sky) had a 40-23 lead at halftime and kept the lead between 14 and 22 throughout the second half.
Idaho kept it close for the first nine minutes, but after Khadim Samb's jumper for the Vandals tied it at 18, Portland State scored 14 straight points and closed the first half on a 22-5 run.
Sal Nuhu had 10 rebounds for the Vikings, who outrebounded the Vandals 38-31.
Idaho was 6 of 23 from 3-point range and got to the foul line for just eight shots, making five.
Hassan Diarra commits to play for Aggies, coach Buzz Williams
Guard Hassan Diarra, who averaged 13.2 points, 4.6 rebounds and 4.1 assists on the Nike EYBL circuit last spring and summer, has committed to Texas A&M and coach Buzz Williams.
White says Nembhard is pretty unique
There are high expectations for guard Andrew Nembhard this season as he exhibits great leadership as a sophomore.
Gators have to get better in order to max out as a team
Florida head coach Mike White and guard Andrew Nembhard join the SEC Now desk to discuss Nembhard's growing leadership.