Four-time Cincinnati semi-finalist Sabalenka will rise to second in the WTA rankings with a week to go before the start of the US Open.
Sabalenka will play Monday's final against the winner of a later match between Spain's Paula Badosa and US sixth seed Jessica Pegula.
Sabalenka had a battle on her hands to close out the win, with Swiatek putting up a huge battle in the closing stages.
Third-ranked Sabalenka led 5-1 in the second set but Swiatek showed why she is ranked atop the WTA table as she repeatedly saved match-winners from her opponent.
Sabalenka was broken for 5-3 but finally claimed the hard-fought victory a game later with a concluding break of Swiatek on a return winner on her 10th match point after nearly two hours.
"I finally broke the barrier," Sabalenka said of her place in the title match.
"It was such a tough battle with Iga, and we also had to be patient with the weather."
Raindrops required the court lines to be dried by towels during several short interruptions.
"On the match points I just had to tell myself that this is why she's world number one and will fight to the last point," Sabalenka said.
"I just had to keep doing the job and hopefully win."
The victory served as revenge for Sabalenka, who lost Masters-level clay finals to Swiatek in Madrid and Rome last spring.
