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.
DouDou Gueye, a 6-foot-10 center from Senegal, has signed with Ball State as a graduate transfer from South Carolina State.
We have changes at the top of the draft and a shakeup in the lottery, with teams starting to make their final decisions. Get the latest in Chad Ford's Mock Draft 9.0.
Duke freshman point guard Derryck Thornton Jr. is transferring to USC, his father announced on Friday to Scout.com.