SYDNEY (AP) — Ons Jabeur retired with a lower back injury in the Sydney Classic quarterfinals on Thursday, allowing Anett Kontaveit to advance.

The fourth-seeded Kontaveit advanced after the seventh-seeded Tunisian lost the opening set 6-4 and decided to stop soon after.

Jabeur received a medical timeout after the set and then attempted to start the second set. But after serving a let and a first-serve fault, she walked to the net for a match-ending hug. She is seeded ninth for the Australian Open, which starts next week.

Jabeur reached the quarterfinals at Melbourne Park in 2020.

“I really hope that Ons is going to be fine for next week and that it’s nothing too serious,” Kontaveit said. “The first set was really competitive and we’ve had some tough matches before, but she’s always come on top. I was really happy to get the set and that I was playing the way I was playing.”

Attempting to reach a fourth straight final, Kontaveit will next face third-seeded Barbora Krejcikova, who beat Caroline Garcia 6-0, 6-2.

Krejcikova has lost only eight games through two matches.

Second-seeded Garbine Muguruza was upset by Daria Kasatkina 6-4, 6-4 in the quarterfinals. The Russian will next face fifth-seeded Paula Badosa, who defeated Belinda Bencic 7-6 (6), 3-6, 6-3.

In the men’s tournament in Sydney, former No. 1 Andy Murray advanced to the semifinals when eighth-seeded David Goffin retired at the start of the second set. Murray took the first set 6-2.

Murray will next face Reilly Opelka. The fourth-seeded American beat Brandon Nakashima 7-6 (4), 6-2.

Top-seeded Aslan Karatsev also advanced to the last four by beating Lorenzo Sonego 6-2, 3-6, 6-2. The Russian, who last year reached the Australian Open semifinals as a qualifier, will next play third-seeded Dan Evans, who beat Maxime Cressy 6-4, 7-6 (5).

At the Adelaide International, former U.S. Open champion Marin Cilic beat Tommy Paul 6-4, 2-6, 6-3 and reached the semifinals for the second straight week.

In a match of strong servers, Cilic served 14 aces to Paul’s eight and won 84% of his first-serve points.

The Croat will next face Thanasi Kokkinakis after the Adelaide native beat Aleksander Vukic 6-7 (5), 6-3, 6-2.

Third-seeded Karen Khachanov, runner-up at the first Adelaide International last week, lost to 58th-ranked qualifier Arthur Rinderknech of France 7-6 (7), 7-5.

Rinderknech’s semifinal match will be against Corentin Moutet, who beat Thiago Monteiro 6-4, 6-4.

In the women’s draw, third-seeded Coco Gauff beat Ana Konjuh 6-3, 6-4. She will next face Madison Keys, who defeated eighth-seeded Liudmila Samsonova 6-3, 3-6, 6-3.

Fourth-seeded Tamara Zidansek beat Lauren Davis 7-6 (4), 7-6 (7) to set up to a semifinal match against Alison Riske, who advanced when Madison Brengle retired at 3-3 in the first set of their match.

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