With the victory, UCI, ranked No. 24 in the nation, climbed to 34-18, 14-7 in the Big West, while the Highlanders dropped to 29-21, 11-10.
Pettis hurled his first complete game of the season to improve to 8-3. The right-hander blanked UCR for seven innings and went on to strike out six, walk two and allow six runs (four earned).
The Anteaters gave Pettis a four-run lead in the middle innings.
Brian Hernandez put UCI on the board in the third inning with a two-out single up the middle to score Sean Madigan who was hit by the pitch and took second on a groundout.
D.J. Crumlich and Madigan delivered in the fourth with back-to-back, two-out hits to give UCI a 3-0 advantage and Ronnie Shaeffer's sacrifice fly to right in the sixth would capitalize on a leadoff double by Francis Larson.
UC Riverside starter Matt Larkins was lifted from the game in the seventh after giving up a two-run home run to Casey Stevenson, his third of the season. Hernandez then greeted reliever Mike Wolford with a solo home run and Drew Hillman belted a two-run homer to left, giving UCI a 9-0 lead, as they became the first Anteater trio to hit three home runs in a single inning.
Hillman was perfect at the plate, with a season-high four for four and two runs batted in.
Hernandez was three for five with two RBIs. Stevenson also drove in two runs while hitting two for five.
Larkins fell to 6-4 after giving up six runs on nine hits in six innings. Tony Nix led UC Riverside with two RBIs.
The Anteaters play at USC in a nonconference game today at 6:30 p.m.
— From staff reports