World number seven Ons Jabeur withdrew from the Zhengzhou Open ahead of her quarterfinal against Daria Kasatkina, blaming a knee injury that hampered her during a hard-fought victory over Lucia Bronzetti on Thursday.
Playing with her right knee taped, the Tunisian three-time Grand Slam finalist failed to serve out the victory on three occasions and needed five match points to movea past the 63rd-ranked Italian Bronzetti 6-3, 7-6 (7/5) in just under two hours.
Shortly after her victory, the 29-year-old Jabeur announced she had to pull out of the tournament, handing Kasatkina a walkover into the semi-finals.
Eighth seed Kasatkina beat home player Bai Zhuoxuan 6-2, 6-4.
Having qualified for the WTA Finals for a second consecutive year, Jabeur faces a race against time to be ready for the prestigious season finale, which kicks off in Cancun on October 29.
“I’m so sorry that I have to withdraw because my knee is not feeling so great. I just want to say that I love my time here in Zhengzhou and I hopefully I can come back next year,” said the fourth seed.
Kasatkina also had to overcome a second-set fightback from her opponent and needed four match points before she completed a 90-minute victory over 117th-ranked Bai.
The 26-year-old Russian, who has lost her last five matches to Jabeur, will now move directly into the final four, where she awaits former French Open champion Barbora Krejcikova or Ukrainian Lesia Tsurenko.