Fotu, who came into the game leading the Big West Conference in field goal percentage (.608), connected on 10 of 13 field goals and 6 of 8 free throws.
Hawaii (16-7, 5-4 Big West), which trailed for the majority of the first half, used a 13-3 run that bridged the two halves to open up a 34-24 lead with 19:40 remaining. The Rainbow Warriors wouldn't trail again.
Brian Bennett hit a jumper to pull Cal Poly (8-14, 4-5) within 54-53 with 6:30 left but the 'Bows used a 10-2 run over the next 5:39 to put the game away.
Christian Stanhardinger scored 18 points and grabbed 12 rebounds in the win.
Dave Nwaba and Kyle Odister scored 12 apiece for Cal Poly, which shot 38.6 percent.