Tanner Krebs had 14 points and seven rebounds for Saint Marys (10-7, 1-1 West Coast Conference).
Fitts scored the Gaels first 10 points — including three 3-pointers in an 82-second span — in a 17-4 spurt that made it 42-29 before TJ Haws hit a 3 to pull the Cougars within 10 at the break. Yoeli Childs scored BYUs first eight second-half points to trim the deficit to 49-40 with 16:55 to play but Saint Marys scored 10 of the next 13 points to push the lead into double figures for good.
Childs had 21 points and 12 rebounds, his 10th double-double this season, and Haws scored 20 for BYU (9-8, 1-1).
Saint Marys shot 55 percent from the field, committed just seven turnovers and had 10 steals.