Madison Keys saw off France's Pauline Parmentier to fire the United States into the Fed Cup final where the Czech Republic lie in wait for the defending champions.
Keys, 13th in the world, defeated the 122nd-ranked Parmentier 7-6 (7/4), 6-4 to earn the US a 3-1 win in Aix-en-Provence.
Sloane Stephens had put the US on the verge of the final after brushing aside Kristina Mladenovic 6-2, 6-0 in today's first rubber.
It was world number 20 Mladenovic who had given France a fighting chance when ending Coco Vandeweghe's 13-match Fed Cup win streak to pull France level at 1-1 on Saturday.
But she was unable to repeat those heroics against the US Open champion who had given the Americans their first point when defeating Parmentier 7-6 (7/3), 7-5 in Saturday's opening match.
Earlier, Petra Kvitova put the Czech Republic into a sixth Fed Cup final in eight years following her win against Angelique Kerber in the other semi-final in Stuttgart.
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Kvitova, a two-time Wimbledon champion, needed just 58 minutes to power her way to a 6-2, 6-2 win over Kerber and give the Czechs an unassailable 3-1 lead over Germany.
After the Czechs had gone 2-0 up on Saturday, Julia Goerges had given hosts Germany a brief lifeline by beating Karolina Pliskova before Kvitova's decisive win.
"I am very relieved. I was getting nervous before this game," admitted Kvitova.
"We had a great position from yesterday, I think Julia played a really good match.
"I knew we still needed one point from our last two games and I just did my best."
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