Fulton was 7 of 9 from the floor for the Tigers (14-10, 8-4 Big West), who shot 50 percent from the floor and won despite committing 18 turnovers. De Souza made three of Pacific's seven 3-pointers.
Stephan Hicks and Stephen Maxwell scored 16 apiece for the Matadors (13-13, 4-10), who couldn't avenge a Jan. 19 home loss to Pacific. Hicks and Maxwell were a combined 12 of 20 from the floor, but their teammates were 7 of 29.
Pacific never trailed and led by as many as 16 in the second half, but CS Northridge pulled within 58-54 on Josh Greene's free throw with 1:17 to play. De Souza went 6 of 6 from the free-throw line in the final 40 seconds to seal the victory.
Pacific's bench outscored Northridge's, 29-5.
Andrew White III will return to the Nebraska men's basketball team next season after removing his name from the NBA draft.
Mike Brey is looking at former Notre Dame players to fill two assistant jobs that have opened up with the departures of Martin Ingelsby and Anthony Solomon.
Purdue's 2016-17 prospects got a jolt Wednesday when forward Caleb Swanigan announced he will return for his sophomore season.