The Hoosiers shot 70 percent from the field while bouncing back from their first loss of the season, an 88-86 upset at the hands of Butler last Saturday that knocked Indiana out of the No. 1 spot in the national rankings.
The 7-foot Zeller made 7-of-9 from the field and scored 16 points. Watford added 15 points while grabbing eight rebounds.
Indiana (10-1) grabbed a 46-29 halftime lead and held Mount St. Mary's to 31 percent shooting. Of the 17 field goals made by the Mountaineers (4-5), nine came from 3-point range.
Mount St. Mary's was led by Rashad Whack with 17 points.