Top seed Jessica Pegula survived a tough test to beat Ekaterina Alexandrova 6-2 2-6 7-5 in a topsy-turvy Charleston Open semifinal on Saturday and will face compatriot Sofia Kenin in her fourth championship match of the season.
Pegula had looked as though she would roll through the match as she won the first five games but had to find another level after Alexandrova fought back and the American clinched it with a superb backhand winner down the line.
Later on Saturday, Kenin advanced as opponent Amanda Anisimova retired with injury in the first set.
"That was a tough match," Pegula told the Tennis Channel.
"It wasn't the prettiest at times, it was really windy, there were some awkward shots, we were both very uncomfortable, I feel like, on some short balls, some low balls, it was kind of swirling in the wind so it was just trying not to get frustrated, having to move your feet a lot and just competing."
Pegula broke her opponent in the first game with a backhand winner before Alexandrova helped the American to another break in the third game with a double fault and a clumsy shot that sailed past the baseline.
They traded breaks in the fifth and sixth games before the 26th-ranked Russian improved her form across the board in the second set, as she broke Pegula with a fine forehand shot in the sixth game and again with a forehand winner on set point.
They traded breaks three times in the final set before Pegula forced her opponent into an error on break point with a perfectly placed backhand at the net in the 11th game to close out the two-hour 21-minute-long marathon match.
It was Pegula's 24th match win this year, the most in the WTA.
Anisimova had hoped to build on a strong start this season after she ended a three-year title drought in Doha in February but the afternoon quickly derailed for the eighth seed.
With Kenin up a break in the fourth game, Anisimova stopped up short and began moving gingerly around the court before asking for the physio with the score tied 30-30.
She lay on her back as tournament staff tended to what appeared to be a hip injury and tried to carry on from there but she could not keep up the fight and retired with Kenin up 5-2 in the set.
It will be the first time that the Charleston Open, the largest women's-only tennis tournament in North America, will see an All-American final since 1990.