UC Riverside (5-3) made 35 of 54 field goal attempts (64.8 percent) while limiting the Vikings to 21-of-48 shooting (43.8 percent).
The Highlanders trailed early but came back to take a 37-32 halftime lead. Johns hit a jumper to open the second half with a 10-0 run and the Highlanders never looked back, leading 60-43 at the midway point of the final period.
Jaylen Bland, who nailed 3 of 6 from beyond the arc, scored 17 points, Steven Thornton added 14 and Nick Gruninger finished with 12 for the Highlanders. Steven Jones had nine points and six assists.
DeShaun Wiggins scored 17 points and Gary Winston added 15 for Portland State (4-3), which has lost its last three games.