Great Britain will have to come from behind to reach the Billie Jean King Cup final after a battling Sonay Kartal fell to the United States' Emma Navarro to go 1-0 down.
Kartal, ranked more than 60 places below world number 18 Navarro, had looked on course for her third victory over a player ranked inside the top 20 this year after going a set and a break up.
But Navarro, who saved two set points against Kazakhstan's Yulia Putintseva in the quarter-finals, fought back to outlast Kartal 3-6 6-4 6-3 and give the US the lead.
The loss means Katie Boulter must beat world number seven Jessica Pegula to keep Britain in the tie.
Britain, competing in the semi-finals for the third time in four years, are attempting to qualify for the final for the first time in 44 years.
They have never won the women's team competition, while their American opponents are 18-time champions.