Keothavong made an encouraging return to WTA action in Memphis
Britain's Anne Keothavong failed to reach her first WTA Tour final as she lost to Swedish qualifier Sofia Arvidsson in the Cellular South Cup.
The Londoner went down 6-4 4-6 6-4 as she bowed out in the semi-finals in Memphis for the second straight year.
Keothavong, 26, was playing in her first WTA tournament after over six months out with a knee injury.
"It wasn't to be," she said. "It's been a long road back and I have to put everything into perspective."
The British number three told her website: "Sofia was the more consistent player but I felt like the more aggressive and powerful player except I wasn't able to string my good stuff together for long enough at a time.
"My first serve let me down today but it's something I've struggled with all week and it's going to need some work before my next tournament at Indian Wells.
"The fire is still there. I fought my hardest and I'm only going to get better the more I play from now.
"There's been a lot of tennis this month and I need to allow some time for my body to recover again. There's a lot I can build on and that's exciting for the rest of the year."
Top seed Maria Sharapova won the second semi-final, seeing off fifth seed Petra Kvitova 6-4 6-3.
In the men's event, defending champion Andy Roddick suffered a surprise 7-5 3-6 6-1 defeat by fellow American Sam Querrey in the quarter-finals.
Querrey goes on to face Ernest Gulbis, while Germany's Philipp Petzschner will play sixth seed John Isner in the other semi.