Jessica Pegula rallied in the third set to topple defending champion Iga Swiatek and book a title showdown with Coco Gauff at the ATP-WTA Cincinnati Masters.
World No 3 Pegula won a "crazy" match against Swiatek 7-5, 4-6, 6-4.
Gauff powered past giant-killer Sara Bejlek 6-4, 6-1, ending the unseeded Czech's dream run that included a fourth-round victory over world No 1 Aryna Sabalenka.
Their all-American Sunday night final will a men's title clash featuring American Frances Tiafoe and Arthur Fils of France.
Fils charged into his first Masters 1000 final with a 6-3, 6-4 victory over French Open runner-up Flavio Cobolli in a match delayed for 45 minutes by rain and lightning.
Swiatek and Pegula then waited out another rain delay before their match, which was also briefly interrupted two games in.
"Crazy match today," Pegula said after needing nearly three hours to subdue Swiatek, who was coming off her first title of 2026 in Toronto last week.
"A lot of back and forth, a lot of breaks," she said, "Really windy, kind of odd conditions. I felt like we were playing well and then not playing well.
"It was really tough to kind of get a gauge on the match."
The two rode a rollercoaster of breaks and re-breaks before Pegula took a 5-4 lead in the final set, Swiatek saving three break points before double-faulting on a fourth.
Pegula quickly closed it out, firing a service winner on match point.
"I was just really happy with the way I was able to kind of handle just a lot that was going on today," the 31-year-old American said. "I did a good job of no matter what was happening."
The first five games of what evolved into an epic went against the server as Pegula and Swiatek struggled to adjust to the conditions.
Swiatek blinked first as Pegula held at love for a 4-2 lead, but Swiatek won the next three games before Pegula broke again, finally taking the set when Swiatek smacked a volley into the net on set point.
They had exchanged two breaks in the second when Swiatek broke in the final game to square the match.
Swiatek leaves for the US Open starting on August 30 with a good feeling about her game despite the defeat.
"We made some steps forward in this intensive part of the season," the six-time Grand Slam champion said. "It was tough to play today with the wind, but we each put pressure on the other. I didn't feel good in the first set but coming back in the second and using all of my chances was a good change."
Gauff, the 2023 Cincinnati champion, got off to a hot start against Bejlek, jumping to a 4-1 lead. Bejlek fought back to 4-4, but the American regained her rhythm to close out the set and run away with the second.
"I tried not to take my foot off the gas because I knew at any moment she could come back," Gauff said.
'DAMN GOOD'
Tiafoe, runner-up to Jannik Sinner in Cincinnati in 2024, returned to the final with a 7-5, 6-3 victory over fellow American Brandon Nakashima.
Tiafoe saved three set points in the opening set, breaking Nakashima five times in all to earn the win in less than two hours.
"It feels damn good," Tiafoe said.
The American predicted a "hell of a show" against Fils, whose 68-minute win over seventh-seeded Cobolli made him the youngest French Masters finalist since a 20-year-old Richard Gasquet in Toronto two decades ago.
Fils admitted he had been unsettled by the weather delay.
"You come on court more nervous because it's a semifinal. The rain arrives, you wait, and when you come back conditions are completely different," he said.
"It was tough but I'm happy with how I dealt with it."