To begin the 24-8 run, Portland State (8-16) trailed 50-42 and scored 10 straight points capped off by a Harthun 3-pointer which gave the Vikings a 52-50 lead with 7:51 remaining in the game. Portland State never trailed again.
Chris Patton had 22 points on 9-of-17 shooting and grabbed five rebounds for UC Riverside (6-21), which shot 44.4 percent from the floor but was only 2 of 14 from three-point range. Josh Fox had 10 points and 12 rebounds.
The Highlanders outscored Portland State 36-20 inside the paint.
Gary Winston scored 10 points and had three assists for the Vikings, which were 18 of 23 from the free-throw line.