The Spartans completed their first week as the nation's top-ranked team with a solid performance that included nine 3-pointers in 18 tries.
Appling, Adriean Payne and Branden Dawson are usually in Michigan State's starting lineup, but they began the game on the bench due to a reported classroom attendance issue.
Travis Trice contributed 15 points in his first career start. The Spartans improved to 7-0 and will next be in action against North Carolina Wednesday.
Mount St. Mary's (2-6) was led by Will Miller with 15 points.
It was the second time in school history that the Mountaineers had faced a No. 1-ranked team. They lost to North Carolina to open the 2008 NCAA Tournament when the Tar Heels were at the top of the rankings.