Madrid, Spain (SportsNetwork.com) - Two-time defending champion Serena Williams pulled out of the draw, while last year's runner-up Maria Sharapova booked a spot in Saturday's semifinals at the $4.2 million Madrid Open, a clay court French Open tune-up.
The current world No. 1 superstar Williams cited a thigh injury as the reason for her pull out on Day 7 in the Spanish capital.
She was hurt during a first-round win over Swiss qualifier Belinda Bencic on Sunday, but continued to play and won two more matches in straight sets before deciding to withdraw prior to her scheduled quarterfinal against 2011 Madrid Open and Wimbledon champ Petra Kvitova.
"I have a left thigh injury and, unfortunately, have to withdraw from this year's Mutua Madrid Open," Williams said in a statement Friday. "It happened during my first round match. It started to get better, but most importantly right now, I just need some time to rest and recover."
Williams beat Sharapova in last year's Madrid finale.
"It's beyond words. It's so frustrating," she added. "We couldn't ask for a better tournament and I love it here in Madrid. I love being a champion here. This is not the way I wanted this week to end."
Williams is still planning to play next week in Rome.
Kvitova received a walkover into the semifinals at the Magic Box, where she'll meet rising Romanian Simona Halep, who won their lone previous matchup.
Meanwhile, the eighth-seeded former world No. 1 Sharapova upended second- seeded Australian Open champion Li Na 2-6, 7-6 (7-5), 6-3 and a fourth-seeded Halep humbled 11th-seeded former No. 1 and former French Open titlist Ana Ivanovic 6-2, 6-2. Sharapova improved to 10-5 lifetime against Li, including wins now in five of their last six meetings.
Sharapova's semifinal opponent will be third-seeded Polish star Agnieszka Radwanska, who was tested by French qualifier Caroline Garcia in a tight 6-4, 4-6, 6-4 decision.
The career Grand Slam champion Sharapova is 9-2 lifetime against Radwanska, including a win in Stuttgart last month.