Junior shortstop D.J. Crumlich had two doubles and one run batted in for the Anteaters (20-8, 4-2 in conference), who won the opening game of the series Friday, before dropping two straight.
Fullerton (23-9, 5-1) was ranked No. 12 by Baseball America.
UC Irvine Coach Mike Gillespie said after Sunday's loss that his team's lack of execution in several areas was embarrassing.
UCI plays host to San Diego State on Tuesday at 6:30 p.m.
Biola 7, Vanguard 6
LA MIRADA — Kyle Hardman went two for three with three runs batted in and Sean Wilson was two for four with two RBIs for the visiting Lions in the Golden State Athletic Conference game Monday.
Vanguard led, 4-2, until Biola scored five in the fourth.
The Lions fell to 17-21, 13-15, while Biola is now 25-14, 19-8.
UC Irvine def.
Cal State Northridge
NORTHRIDGE — Cory Yoder led the visiting Anteaters to their fifth straight victory with a team-best 11 kills in the Mountain Pacific Sports Federation match Saturday.
Yoder hit .556, while Jordan DuFault added eight kills and seven digs and Anthony Spittle collected 30 assists for the then-No. 4-ranked 'Eaters (17-11, 13-8 in conference).
CSUN fell to 7-21, 5-16.
TRACK & FIELD
Big West Challenge Cup
IRVINE — UC Irvine senior Madeline Leduc won the long jump and triple jump to pace the Anteaters Friday at Anteater Stadium.
Leduc leapt 18-81/2 in the long mump and 39-73/4 in the triple jump.
UCI's Breeanca Fleming won the 100 meters in 12.17 seconds and was second in the 200 in 25.17.
Amber Middleton won the 400 hurdles (1 minute, 2.91 seconds) for UCI and was second in the 100 hurdles in 14.10.
Alisha Misiaita won the shot put (46 feet, 91/2 inches) and was third in the discus (139-0).
Ericka Nowell was second in the 400 in 57.74, while UCI teammates Maggie Newton-Neal (2:11.57) and Sakia Sailnuu (2:14.20) were second and third, respectively, in the 800.