Mariana Duque-Marino overcame Varvara Lepchenko and Annika Beck on Friday to set up a meeting with Kiki Bertens in the Nurnberger Versicherungscup final.
Duque-Marino's quarter-final meeting with Lepchenko was postponed due to darkness after a rain-interrupted Thursday.
The world number 98 Colombian staved off four set points but was unable to hold serve and force a tie-break at the end of the first set.
Duque-Marino was three points away from defeat to Lepchenko in a second-set tie-break, but rallied from 4-3 down to force a decider where she completed a 5-7 7-6 (7-4) 7-5 triumph.
Bertens also had to battle from behind to overcome home-hope Julia Gorges.
The Dutchwoman took a 6-2 lead in the third-set tie-break but needed three attempts to claim match point to win 3-6 6-4 7-6 (7-4).
Duque-Marino then returned to the court for her semi-final match against third seed Beck - ranked 56 places above her.
Seemingly unaffected by having already played a full match earlier in the day, the Colombian raced to a 7-5 6-1 victory.