Vaughn was 11 of 15 from the floor, including five makes from 3-point range, for the Titans (15-7, 7-3 Big West). Cal State Fullerton shot 52.5 percent (31 of 59) from the floor, including a school-record 17 3-pointers.
Orlando Johnson had 28 points, James Nunnally 19 and Alan Williams 14 for the Gauchos (12-8, 7-3).
The Titans moved into a second-place tie with UC Santa Barbara in the Big West. The teams split two games this season.
UC Santa Barbara led 47-43 at the break, but the Titans used a 19-6 run to take a 64-55 lead with 13:54 remaining. The Gauchos got as close at eight points, but a 15-5 surge gave Cal State Fullerton a commanding 83-65 cushion with 7:24 to play.
D.J. Seeley scored 15 points and Orane Chin 13 for the Titans.