Indiana (1-0) has now won 13 straight season-openers and 26 consecutive home openers.
The Eagles (0-1) were led by Anthony Banks, who had 16 points, but dropped to 1-10 all-time against BCS schools and 0-4 all-time against the Big Ten.
Florida Gulf Coast hung around for a while, closing to nine early in the second half and getting within 56-44 with 15:50 to go. But Watford answered with six straight points and Indiana never let the Eagles get close again.
Indiana connected on 14 of 28 shots from 3-point range, and Watford finished with five rebounds and four assists.