Kiki Bertens of the Netherlands had to throw in the towel after 24 minutes, setting up a Sunday finals match between Errani and Germany's Mona Barthel.
Barthel advanced Saturday with a 6-1, 6-4 win over Kristina Mladenovic of France.
Errani will seek to regain the momentum she enjoyed last year when she won four titles and was runner-up at the French Open. So far this year, she has only gotten as far as the quarterfinals in one of the three tournaments she has played in.
Errani survived a tough quarterfinal match Friday against Carla Suarez Navarro and made it out of the first round when her opponent retired in the first set.