Anne Keothavong beat Karolina Sprem to secure a Cellular South Cup semi-final place, but Elena Baltacha lost to Maria Sharapova.
Britain's number three, Keothavong, defeated her Croatian opponent Sprem 6-4 6-3 in Memphis to at least match her run to the last four in 2009.
She will now face Sweden's Sofia Arvidsson, who beat second seed Melanie Oudin 6-1 6-3.
However, British number one Baltacha went down 6-2 7-5 to Russia's three-time Grand Slam winner and the tournament's top seed Sharapova.
Meanwhile Estonian third seed Kaia Kanepi defeated fifth seed Petra Kvitova of the Czech Republic 1-6 6-3 7-6 (7-0) in the other quarter-final.