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.
White House officials said Tuesday that the Villanova men's basketball team will visit with President Barack Obama next week.
Kendrick Nunn, who pleaded guilty to misdemeanor domestic battery last week, has been dismissed from the Illinois basketball team.
Delaware has hired Notre Dame assistant Martin Ingelsby as its next men's basketball head coach, sources told ESPN's Jeff Borzello.