Sammie Vandiver's grounder was bobbled by shortstop Briana Perez, allowing Shianne Brannan to score from third and give the Titans a 3-2 victory that pushed the top-seeded Bruins to the brink of elimination.
Fullerton (35-23) needs one more win Sunday to advance to the Super Regionals. UCLA returned Saturday night to face the winner of an earlier elimination game between Texas State and Sacramento State.
After being held in check for four innings by Sacramento State starter Celina Matthias the night before, the third-ranked Bruins (51-5) came out swinging against Titans junior Trish Parks, who threw 112 pitches in a complete-game victory over Texas State in Friday's first game.