CoCo Vandeweghe beat France's Caroline Garcia 6-4, 6-2 to reach her first career clay final at the Stuttgart Grand Prix on Saturday.
The last American to reach a final in Germany's automotive capital was Lindsay Davenport in 2005.
On Sunday, Vandeweghe will face either fifth seeded Czech Karolina Pliskova or Anett Kontaveit of Estonia who meet in Saturday's other semi-final.
The 16th ranked Vandeweghe has proved a revelation this week on a surface that she has never shone on before, seeing off world number one Simona Halep in the quarter-finals.
"I'm playing relaxed, chill," the 26-year-old with a pair of Dutch grass court titles on her WTA curriculum vitae said.
"It's like I'm on the beach in California. I wouldn't say that I don't care, but I'm not taking the matches deadly seriously.
"I'm one step closer to the title (and a flame-red Porsche 718 Boxster cabriolet which has been on display by the court all week).
"I'm excited to be in the final."
Vandeweghe loosened up a tight first set in the ninth game with a break of her French opponent.
The Californian who barely rates clay in her tennis pecking order, earned a set point a game later as she chased a drop shot and produced a volley winner at the net.
Vandeweghe claimed the opener on the next point as Garcia drilled a forehand return wide.
The second set went quickly, with Vandeweghe breaking Garcia twice, taking command at 5-2 from a love break of the French player.
The unseeded America wrapped up victory in the next game with a service winner on match point after 74 minutes.
"I had to strike first," Vandeweghe said. "I needed to make her uncomfortable if I was to have a chance."
She leads the series with Garcia 2-1 and her finals appearance should move her to 14th in the rankings.
CoCo Vandeweghe serves up defeat for Caroline Garcia to book first ever clay court final appearance