The Gaels (4-0) opened the game on a 16-6 run and led by as much as 16 early in the second half before Drake surged back to pull within two with 6:42 remaining.
Stephen Holt hit a 3-pointer and Levesque made a layup to put Saint Mary's ahead by five.
Another layup from Levesque increased the lead to six, and Waldow blocked Karl Madison's ensuing layup attempt with 1:48 remaining.
Carter hit a last-second three to finish with 18 points and Daddy Ugbede added 11.
Waldow had a career-high five blocks and was one of four Gaels to score in double figures.