Keothavong is chasing a first WTA tournament win
Anne Keothavong came back from a set down to win at the Warsaw Open as Maria Sharapova continued her successful comeback from injury.
Keothavong beat American Jill Craybas 3-6 6-3 6-1 to become the first British woman to reach the quarter-finals of a WTA clay-court event since 1990.
"I'm so pleased with the way I kept fighting out there," said Keothavong.
Sharapova, in her second singles game after a nine-and-a-half-month injury lay-off, beat Darya Kustova 6-2 6-0.
She now plays eighth seed Alona Bondarenko for a semi-final place.
Sharapova still had her right shoulder strapped but put in a much more consistent performance than in her first round victory over Tathiana Garbin.
"I thought I did the right things at the right time," said former world number one Sharapova.
"I played a solid game and I did everything I had to do to win."
Keothavong will now play either Julia George, of Germany, or Romania's Ioana Raluca Olaru.
"I'm really pleased to be through to the quarters of a premier WTA event, especially on clay," said Keothavong.
"Jill has been around for a long time. She has plenty of experience and is a tough opponent to break down but I managed to do that by being patient and mixing it up.
"I'm feeling great and looking forward to whoever I play on Thursday."