Mertens advanced to the final with a 6-1 4-6 6-4 victory over tough competitor Vera Lapko.
Mertens, who is currently world No.20, beat Mona Barthel 6-4 5-7 7-6 in the quarterfinal to set up the final-four clash with the Belarusian. She will now play Sabalenka in Sunday's final.
Lapko was victorious in her own quarterfinal earlier on in the day, eliminating Kirsten Flipkens after a 6-4 7-6(4) victory.
Sabalenka advanced to the semifinal stage after beating Camila Giorgio 6-3 6-0.
She then continued her dominate performance in her semifinal after a 6-4 6-2 win over Stefanie Voegele to secure a final berth.
Voegele beat Tamara Korpatsch 6-3 6-3 beforehand to secure her spot in the last four.