Madison Keys on Friday set up an all-American Adelaide International final against Alison Riske while France's Arthur Rinderknech powered into his first ATP Tour decider.
Unseeded former US Open finalist Keys fought back from a set down to end the hopes of teenager and third seed Coco Gauff 3-6, 6-2, 7-5.
She will face Riske, who breezed through when 2021 French Open semi-finalist Tamara Zidansek withdrew with an abdominal injury as a precaution just days away from the opening Grand Slam of the year.
"Coco's a phenomenal player and I knew I was going to have to play some of my best tennis," said Keys who is targeting her fifth WTA title and first since 2019.
Keys and Riske are frequently practice partners and she knows it will need another big effort to get over the line on Saturday.
"We both train with each other all the time, so it's going to be a really tough match. I'm just really happy to start the year off on a really great foot."
World number 31 Zidansek, meanwhile, apologised for pulling out of her clash with unseeded Riske.
"I have played a lot of tennis in the last three days and I am really sorry that today I won't be able to play my semi-final, as I am not fit to play my best tennis," she said.
Rinderknech reached the men's final by sweeping past compatriot Corentin Moutet 6-1, 6-3, and has now won five of his seven matches this year.
The world number 58 was dominant, dropping just three points on his first serve and winning more than half of his return points, forcing 22 unforced errors from his increasingly emotional opponent.
He will face either fourth seed Marin Cilic or in-form Australian wildcard Thanasi Kokkinakis in Saturday's final.
"Of course, I'm really happy with this win and to be in the final tomorrow," said Rinderknech, who represented France at last week's ATP Cup in Sydney.