Agnieszka Radwanska secured the last remaining spot in the season-ending WTA Championships without hitting a ball after Marion Bartoli retired from her Kremlin Cup quarterfinal with an illness on Friday.
Kremlin Cup organisers said the Frenchwoman was forced to withdraw from her match against Russia's Elena Vesnina after suffering from a viral infection.
World number nine Bartoli was the only player with a chance of catching the eighth-ranked Pole but she needed to win in Moscow to clinch a place in the eight-player field in Istanbul.
"I think my whole body needed a break," Bartoli said in a statement. "Yesterday, during my match I already didn't feel very well but I still had energy left so it was enough to win."
The third seed had crushed unseeded Russia Ksenia Pervak 6-1 6-1 in just over an hour on Thursday to reach the last eight.
"This morning I had so much pain in my whole body, in my neck... I couldn't even warm up today. So I knew it would be very difficult (to play today)," added Bartoli, who won her second title of the year on Sunday after beating U.S. Open champion Samantha Stosur in the Japan Open final.
"It has been a very long season and I really tried to play till the very end but that was it for me."
Russia's top seed Vera Zvonareva, who has already booked her ticket to Turkey, was upset by eighth-seeded Slovak Dominika Cibulkova 4-6 6-4 6-4 after nearly a three-hour battle.
Cibulkova now faces Vesnina, ranked number 64 in the world, in Saturday's semi-finals.
Despite losing her opening match in Moscow on Wednesday, Radwanska will join world number one Caroline Wozniacki, Maria Sharapova, Victoria Azarenka, Wimbledon champion Petra Kvitova, Zvonareva, U.S. Open champion Samantha Stosur and French Open champion Li Na in Istanbul next week.