Horn took over last April for retiring coach Dave Odom. Horn promised more intensity from his club and the Gamecocks didn't disappoint in the opener for both teams.
South Carolina began with a 10-0 run and pushed the lead to 18 points less than 11 minutes in.
South Carolina was up 58-32 midway through the second half when Jacksonville State caught fire and used a 27-14 run to cut the lead in half.
However, Holmes hit two straight baskets and Dominique Archie two foul shots to restore control.
Jacksonville State, also in its first game with a new coach in James Green, was led by Brandon Crawford's 28 points.