Mariana Duque-Marino had to play two matches and won them both on Friday to reach the Nuremberg final.
Duque-Marino will seek her second career title against Dutch qualifier Kiki Bertens in Saturday's final.
The Colombian played three sets for nearly three hours in the morning in outlasting Varvara Lepchenko of the United States 5-7, 7-6 (4), 7-2 in a quarterfinal that was postponed on Thursday because of rain.
Duque-Marino needed only just over an hour to dispatch third-seeded Annika Beck of Germany 7-5, 6-1 in the afternoon. Beck was the last seed in the tournament.
In the second semifinal, Bertens came from behind to beat Julia Goerges of Germany 3-6, 6-4, 7-6 (4).
The tournament is a warm-up for the French Open that starts on Sunday in Paris.