Rain washed out Thursday's play so the quarterfinals and semifinals were both contested Friday.
Seppi's first match ended when seventh-seeded Philipp Kohlschreiber retired in the second set with the third-seeded Seppi up 7-5, 2-1. He went on to a 7-5, 6-1 win over Ryan Harrison in the semifinals.
The first set versus Harrison was fairly even but the second turned into a rout as Seppi limited Harrison to just five points when serving.
Roddick, the No. 6 seed, outlasted Fabio Fognini 6-3, 3-6, 7-5 in the quarterfinals and was up 6-3, 3-1 in the semifinals when Steve Darcis retired. Roddick, despite having his serve broken once, had lost only nine points in seven games serving when the match was stopped.
Roddick will be looking for his 31st ATP title in Saturday's final. His most recent came February 2011. Seppi is 2-1 in tournament title matches. He picked up his first ATP title last year at the AEGON and won in Serbia last month.
Roddick won in straight sets in the 2008 U.S. Open third round the only time he played Seppi.