Los Angeles - American seventh seed Sloane Stephens reached the final of the Charleston clay court tournament on Saturday when Australian Open champion Angelique Kerber was forced to quit their semi-final.
Top seed Kerber of Germany was down 6-1, 3-0 when she retired because of a viral illness.
"I had no idea," said Stephens, will battle for the title against Russian Elena Vesnina, a 6-4, 4-6, 6-2 winner over fifth-seeded Sara Errani of Italy.
Stephens, with titles in Auckland and Acapulco already in 2016, had won just one match in five prior appearances on the green clay in Charleston.
Although Kerber's sudden departure cut short her day, the American was pleased with her game to that point.
"It was clear from the beginning what I wanted to do," said Stephens, who hit 14 winners and broke Kerber four times.
"I executed from the start. The wind was crazy today. It's definitely tough to play in the wind, but it's tough for both of us. To be able to come here and win matches in a place that I've never really done well, that feels really good.
"When I go on court, (I try) to give my best, and for sure I wasn't 100 percent today," she said.
Vesnina, a former world number 21 who reached the Charleston final in 2011, had to come through qualifying this year.
She toppled second-seeded Swiss Belinda Bencic in the second round and by reaching the final is projected to rise from 85th in the world to the top 55.
If she can nab her first title since Eastbourne in 2013, the resurgent Russian is projected to break into the top 40 in the rankings.