Drew Petersen added nine points and eight rebounds for USC (7-3).
The Titans missed six consecutive shots and committed three turnovers over the first five minutes as USC scored the first 13 points and Reese Dixon-Waters made a driving layup that gave the Trojans a 22-5 lead midway through the first half.
Latrell Wrightsell Jr., the only Fullerton play to score in double figures, had 17 points.
Fullerton (4-5) shot just 27.6% (8 of29) in the first half but the Trojans scored just one point during a stretch of five-plus minutes and the Titans used a 16-5 spurt to trim their deficit to 27-21 late in the first half, but got no closer.
Johnson made a layup that gave USC a 37-26 lead with 17 minutes to play and Fullerton trailed by double figures the rest of the way.
USC, which went into the game allowing its opponents to shoot just 37.4% from the field (No. 23 nationally), limited Fullerton to 33% shooting (19 of 58).
CSU Fullerton returns home to take on Southern Utah on Saturday
Southern California plays the third of four consecutive home games against Long Beach State next Wednesday
- Gregory Nixon
- Tom Nally
- Tommy Nunez