Harriel added eight rebounds and five assists to his point total.
The Highlanders (1-3) shot nearly 53 percent from the field, making 37 of 70 shots, but Whitman (0-2) hung around thanks to 11 made 3-pointers and the efforts of Ben Eisenhardt who scored 21 points on 7-of-19 shooting while pulling eight rebounds.
Robert Smith was the third player in double figures for UC Riverside with 17 points on 7-of-11 shooting including 3 for 6 from behind the arc. Lucas Devenny scored only three points but had 15 rebounds for the Highlanders.
UC Riverside dominated the paint, outscoring the Missionaries 40-24 and was stellar in the open court, outscoring Whitman 20-5 on fast-break points.
Seton Hall sophomore Isaiah Whitehead will stay in the NBA draft and not return for his junior season.
Washington State's trio of Josh Hawkinson, Conor Clifford and Ike Iroegbu have withdrawn from the NBA draft and will play their senior season with the Cougars.
Gonzaga center Przemek Karnowski, who missed most of last season with a back injury, says he is returning for another year.