Big-serving Isner made light work of the opening set, claiming two breaks of Seppi's service game to record a 6-2 success.
Neither player managed to record a break of serve in the next set, resulting in a breaker being required to determine a winner. Italian Seppi prevailed as the eventual victor by seven points to five.
The deciding set saw both players hold their service games during the opening exchanges.
However, Seppi managed to break Isner late in the contest to wrap up the win courtesy of a 7-5 triumph.