Tyler Lamb added 13 points for the third-seeded 49ers (15-16), who will find out their opponent for the semifinals following the completion of the two other quarterfinal bouts. Travis Hammonds chipped in 12 points and AJ Spencer had 10.
Alex Harris finished with a game-high 17 points, Michael Williams chipped in 10 on just 3-of-17 shooting and Marquis Horne cleared 10 boards for the sixth- seeded Titans (11-20).
In the first half Long Beach State connected on 44 percent from the floor and held Cal State Fullerton to 26.7 percent shooting. The 49ers led 29-25 at the break.
Long Beach State built on its lead in the second half when it shot 52.6 percent from the field. The Titans did nail six 3-pointers in the frame, but were outscored 13-1 at the free-throw line.
Cal State Fullerton lost despite a 27-18 scoring edge from beyond the arc.