Defending champion Errani gained one of the finals spots with a 6-4, 6-4 victory over fourth-seeded Czech Klara Zakopalova.
The top-seeded 26-year-old, who won the Palermo event in 2008, hasn't dropped a set this week and will be gunning for her eighth career WTA singles title.
Her doubles partner Vinci advanced with a 5-7, 6-2, 6-2 defeat of Spaniard Estrella Cabeza Candela.
The 30-year-old will be looking to snap a streak of five straight losses to Errani and lock up her ninth career title as the two face off in the second all-Italian final in tournament history.
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