Amsbaugh had 14 points and eight rebounds off the bench for the Storm (5-3). Simpson led by as many as 24 in the second before Saint Mary's put together a late run.
Quashingm Smith-Pugh scored 18 points to lead the Cardinals (4-4).
Simpson led 32-27 when Amsbaugh made three-straight layups to give the Storm a 38-27 lead with 57 seconds left in the first half. Skaar hit a 3 to open the second half and DJ Dafney went coast-to-coast after a steal as Simpson opened up a 45-29 lead.
Up next: Simpson hosts Monmouth (Ill.) on Monday, Dec. 21. Tipoff is set for 3 p.m.