Luke Nelson chipped in 14 points and Alex Young added seven assists for the top-seeded Anteaters (23-10), who will face seventh-seeded Cal Poly on Friday in the semifinal round.
Nick Gruninger had 10 points, while Taylor Johns cleared seven rebounds for the eighth-seeded Highlanders (10-21).
UC Irvine shot 50 percent from the field in the first half as it led 34-22 at the break. UC Riverside made 33.3 percent of its field goal tries, including just 1-of-6 from 3-point range, not to mention a disappointing 5-of-10 at the free-throw line.
The Anteaters struggled in the second period as they connected on 38.5 percent of their shots from the floor, but the Highlanders did even worse as they converted 25.9 percent over the final 20 minutes. UC Irvine dominated the half, never leading by less than 12 points.
UCI dominated play inside as it outscored UCR 34-12 in the paint.