Injured Marion Bartoli will need to recover fitness when she plays American Christina McHale, who lined up a Friday quarter-final at the WTA event with a 4-6, 6-4, 6-4 win over Misaki Doi.
The top-seeded Bartoli, of France, struggled in a second round win Wednesday over American Vania King as she needed treatment on her left hip.
The world number 10 is counting on solid hardcourt performances this summer in North American as she misses the London Olympics due to a longstanding feud with the national federation over her insistance that her father should be her only coach.
Bartoli spent Thursday in rehab with the hopes of being ready for McHale, one of two American Olympians in the quarter-finals.
"I will be able to rest and have good work on it from the physio and get my whole body loose and relaxed," Bartoli said after her late-night Wednesday win which included a staggering 18 double-faults.
"It is great to have a day off, that's for sure. But I will have to figure out why my serve is not on right now."
McHale showed her fighting qualities as she recovered to beat Doi after nearly three hours, with the 27th-ranked winner reprising a victory over her opponent from Stanford two years ago.
Japan's Doi put McHale under pressure on serve, but the American saved 16 of a massive 19 break chances to reach her second quarter-final of the season after Doha.
"I have to give credit to Misaki because she played really, really well." said the winner. "She made it hard for me. In the third set I started finding my rhythm more on my serve, which made it easier then for me to hold."
Ursula Radwanska, younger sister of Wimbledon finalist and world number two Agnieszka, posted a 6-2, 6-1 win over American Melanie Oudin, who came into the draw as a lucky loser form qualifying.
Radwanska needed just 65 minutes to advance, going through with four aces and five breaks of her opponent.
"I was playing very good today, and serving especially well," said Radwanska, who will play singles plus doubles with her sister for Poland at the Games. "To be honest, I didn't have any strategy because I never played her, so I didn't know what to expect.
"I was just focusing on myself and trying to do my best and go for my shots and keep the serve. I'm happy I did well."
Second seed Dominika Cibulkova of Slovakia defeated New Zealand's Marina Erakovic 6-2, 6-4.