Iga Swiatek progressed to the Cincinnati Open semi-finals as Elena Rybakina sustained a worrying ankle injury.

Following Aryna Sabalenka's shock exit on Wednesday, Rybakina went into her quarter-final tie against Swiatek knowing she needed just two wins to become world number one ahead of the US Open.

Instead, she was forced to retire due to injury while trailing 4-1 in the opening set.

Rybakina called for a medical timeout at 40-40, but she played only one more point before deciding not to push herself any further.

"Of course I feel not the greatest, I couldn't even push from the serve," Rybakina said.

"It's painful to walk. We'll know more tomorrow when we have the MRI. It's been bothering me for a long period of time, but felt like I had it under control.

"It was feeling OK before the match but unfortunately one wrong movement, one landing, and something happened."

It marked Swiatek's second victory over Rybakina in a week, after her triumph in the Canadian Open final.

The Pole will now take on Jessica Pegula, who beat Amanda Anisimova.

Rybakina, meanwhile, will hope to return to fitness in time to contest the final grand slam of the season, which starts on August 30.

24 - Iga Swiatek has equalled Victoria Azarenka for the third-most WTA-1000 semi-finals reached (24) since the format’s introduction in 2009. Podium.#CincyTennis | @CincyTennis @WTA pic.twitter.com/FZYgAnnFoV

— OptaAce (@OptaAce) August 20, 2026

Swiatek equals more records

This will not have been the way Swiatek wanted to win, and she was quick to send her best wishes to Rybakina.

"I hope Elena will be fine. The next tournament is the priority. I know this one is important as well. But US Open is US Open," Swiatek said.

"I hope she's going be ready for that. She's super close to being number one in the world.

"It's a shame. I thought we were playing a good match, but health is a priority. I hope she's going to be OK."

But Swiatek is nevertheless now just one win away from reaching back-to-back finals, and she is hitting form at the right time.

The six-time major champion has equalled Victoria Azarenka for the third-most WTA-1000 semi-finals reached (24), since the format's introduction in 2009.

She has also become the player with the joint-most consecutive semi-finals reached at the Cincinnati Open in the Open Era (four, 2023-2026), equalling Simona Halep (2015-2018).