Former champions Ana Ivanovic and Maria Sharapova advanced to the semi-finals of the Indian Wells WTA tournament in sharply contrasting fashion on Thursday.
Serb Ivanovic completed a 6-3 6-4 upset over ailing seventh seed Marion Bartoli of France while Sharapova battled back from a set and break down to beat fellow Russian Maria Kirilenko 3-6 7-5 6-2 after a wildly fluctuating encounter.
Fifteenth-seeded Ivanovic, the 2008 champion, and second seed Sharapova, who triumphed here in 2006, will meet in the last four at the Indian Wells Tennis Garden on Friday.
World number one Victoria Azarenka of Belarus will face 18th-seeded German Angelique Kerber in the other semi-final, both having played their quarter-finals on Wednesday.
In dazzling desert sunshine, Ivanovic broke Bartoli, last year's runner-up, three times before wrapping up her quarter-final win in one hour 17 minutes when her opponent pushed a forehand service return wide.
The elegant Serb, who had ousted defending champion Caroline Wozniacki in the previous round, seized control with her powerful serving and strong baseline game after being broken in the first game of the match.
"I'm definitely very happy to be through and get my revenge for last year in the quarters," Ivanovic, who was beaten by Bartoli in straight sets at the same stage 12 months ago, said.
"I really knew I had to be aggressive. She does strike the ball a lot harder than maybe it looks."
Ivanovic, who repeatedly clenched her left fist to celebrate points won, felt her service break in the eighth game of the first set had paved the way for her win.
"That was kind of a turning point because after that we both played really solid," said the 24-year-old Serb, who became world number one for the first time after claiming her maiden grand slam singles crown at the 2008 French Open.
"That game I really stepped up another notch, I really stayed low and I was aggressive with my feet."
Bartoli was evaluated by doctors courtside when trailing 1-2 in the second set and said she had succumbed to the viral infection that has already forced eight players to withdraw from Indian Wells.
"The more the match was going on the worse it was getting for me," the 27-year-old added. "I was having a lot of joint pains and feeling shaky and very cold.
"I just tried my hardest under the circumstances, tried to not to retire during the match and still show everyone that I could complete the match," said the Frenchwoman, who has beaten Ivanovic three times in eight career meetings.
Sharapova, who had been the only player left in the draw yet to drop a set, initially struggled on her backhand and was broken twice in the first six games before losing the opening set to Kirilenko in 44 minutes.
She leveled the match after battling through a tight second set, where Kirilenko was penalized a point for hindrance after tapping her racket on the ground three times, and broke her opponent in the second and fourth games of the third to race 4-0 up.
Though Sharapova lost serve in the fifth when she pushed a backhand wide, she broke Kirilenko in the eighth when her opponent double-faulted to seal victory in three hours, five minutes.
"I tried to keep my head up high today even though I wasn't playing my best tennis," said Sharapova, who was beaten by Kirilenko when they last played in the first round of the 2010 Australian Open.
"I was just trying to find my rhythm a little bit on everything, movement and playing wise. Little by little, I started feeling better. Towards the end I really got my groove back, so that was good."