The Gauchos (13-4, 2-2 Big West) snapped a two-game losing streak, shot a season-best 64.8 percent and handed the Titans (10-5, 1-3) their first conference loss of the season.
Josh Akognon led Fullerton with 17 points but shot just 3-for-16 from the floor and only made just one of his 11 3-point attempts.
UC Santa Barbara led for the final 36 minutes, taking the lead 15-10 after an 11-2 run. They led by as many as 12 in the first half, and 15 in the second.
Cal State Fullerton scored 11 unanswered points to pull within four at 49-45 early in the second half, but Joyner hit a 3-pointer, Harris hit two free throws and the Titans would get no closer than seven the rest of the way.