In the women's semi-finals, French qualifier Caroline Garcia survived two rain breaks and advanced to the final by defeating Aryna Sabalenka 6-2, 4-6, 6-1.
Garcia will play for the title on Sunday against Czech Petra Kvitova, who constructed a 6-7 (6/8), 6-4, 6-3 comeback triumph over American Madison Keys.
Garcia is the first qualifier to ever reach the championship match at a Masters tournament.
Kvitova, a two-time Wimbledon winner who played the semi-finals in 2012 and 2018, will be aiming for her 30th career title in her first Cincinnati final.
Garcia maintained control over sixth seed Sabalenka in their contest, where the weather interruptions totaled four hours. She broke six times in a match comprising two hours of actual play.
"What a day it has been," number 35 Garcia said. "Last night I was excited to be in the semi-finals.
"Aryna is a difficult opponent, so fast, so strong. We had a lot of very tough rallies and tough weather. You never knew when you would be coming back to the court — but we managed it."
Kvitova, 32, needed two hours and 20 minutes to eliminate Keys.
"It was an incredible match. I expected it to be tough — but not this tough," Kvitova said. "I got emotional at the end, the match was mentally so tough."
She will make a return to the ranking top-20 after finishing with 24 winners and 16 unforced errors.