Strasbourg, France (SportsNetwork.com) - Top-seeded American Madison Keys pulled out of her scheduled quarterfinal match, while her fellow countrywoman Sloane Stephens upset former world No. 1 Jelena Jankovic at the Strasbourg International, a final clay-court French Open tune-up.

France's own Kristina Mladenovic received a walkover into Friday's semifinals when the Australian Open semifinalist Keys decided against playing on Day 5.

Stephens, meanwhile, was leading the second-seeded Jankovic 6-1 after one set when the Serbian veteran retired at Strasbourg Tennis Club.

Two other quarterfinals saw third-seeded Aussie Samantha Stosur hold off her training partner Ajla Tomljanovic of Croatia 6-4, 3-6, 6-4 and French journeywoman Virginie Razzano overcome Russian Elena Vesnina 4-6, 6-1, 6-1.

The semis will pit the former U.S. Open champion Stosur against Stephens and Mladenovic versus the wild card Razzano in an all-French affair.

"The next match is going to be very difficult and I have to be 100-percent focused on that," Stosur said of her pending bout against Stephens. "I need to go out there and play and if I find myself in the final that'll be fantastic and I'll be very excited. So far I'm playing well."