Karin Knapp outlasted top-seeded Sara Errani 7-6 (4), 4-6, 7-5 to set up a final against Australia's Samantha Stosur at the Gastein Ladies on Sunday.
The all-Italian match was moved from Saturday because of rain. The final will be played later Sunday.
The 43rd-ranked Knapp rallied from 3-0 down to take the opening set in a tiebreaker.
Errani, who is ranked 19th, broke three times to take the second set and fought back from 5-2 down in the final set before Knapp won the last two games.
The second-seeded Stosur defeated Anna Karolina Schmiedlova of Slovakia in straight sets in the first semifinal Saturday.
Knapp and Stosur, who have not played each other before, are both looking for their second title of the season.