Brad Waldow added 14 points and Aaron Bright had 13 with 7 assists for the Gaels (17-4, 9-1 West Coast Conference). Garrett Jackson had 10 rebounds as Saint Mary's had a 33-24 advantage on the boards.
Godwin Okonji had 14 points and Ayodeji Egbeyemi added 10 for the Lions (6-16, 2-8).
Saint Mary's closed the first half on a 13-4 run, with Carter, who had 12 points, hitting three straight 3s, for a 35-32 lead.
Egbeyemi opened the second half with a trey to tie the game, but Desmond Simmons responded with a jumper and Carter hit 3 allowing the Gaels to steadily pull away.
Waldow was 6 of 8 from the field and Carter 6 of 9 as the Gaels shot 50 percent, 11 of 23 behind the arc.