The No. 1-seeded Errani, who won this tournament in 2008 and 2012, rallied from 3-1 down in the second set to beat fourth-seeded Klara Zakopalova of the Czech Republic 6-4, 6-4.
Vinci, Errani's doubles partner, beat Spaniard Estrella Cabeza Candela 5-7, 6-2, 6-2 to reach her first Palermo final.
The second-seeded Vinci recovered from a slow start to cruise through the second set.
In the fifth game of the final set, she broke at love after a double-fault from Candela. Vinci went on to win the next three games and the match.