Last year's champion and World No. 1 Elena Rybakina is through to the Ningbo quarterfinals after Polina Kudermetova retired five games into their second-round match Thursday night.

Rybakina led 5-0 after 30 minutes before Kudermetova was forced to stop. She called for the physio at 3-0 and attempted to play through the issue before retiring. An emotional Kudermetova left the court afterward.

"Definitely not the way I wanted to finish the match," Rybakina said in her on-court interview. "I think Polina, before, she played some tough matches and conditions here are not easy. The balls are quite heavy. I just wish her a speedy recovery and hope it's nothing too serious."

After a season-long race, the world's top players converge in the California desert with the WTA's biggest title still to be won.

Despite the unfortunate ending, Rybakina advanced to the quarterfinals after spending just 30 minutes on court as she continues her title defense.

She will next face Katarzyna Kawa in their first WTA Tour Driven by Mercedes-Benz meeting after the 33-year-old upset No. 5 seed Belinda Bencic 7-5, 6-2 in 1 hour, 43 minutes earlier Thursday.

In a section of the draw that included Jelena Ostapenko and Bencic, Kawa has emerged as a surprise quarterfinalist. The Pole is No. 128 in the PIF WTA Rankings and reached a career-high No. 112 in November 2020. She has reached two WTA finals -- at Jurmala in 2019 and Bogota in 2025 -- and captured her first two WTA 125 titles earlier this year, including one in Huzhou, China, in May.

Kawa has also won five WTA 125 doubles titles, reaching a career-high ranking of No. 64.

The veteran made her WTA Tour qualifying debut at Warsaw in 2010 at age 17. The win over No. 14 Bencic was the biggest of Kawa's career and her first against a Top 20 opponent.

"I felt pressure all the time from the beginning until the end," Kawa said in her on-court interview. "I think the key was that I stayed brave and I made really good shots on important points and that got me through to the finish line.

"I don't really have expectations. This was my biggest win of my whole career so far in singles, so I'm just incredibly excited for this tournament and my next match. Let's see how it goes. I hope it goes well."

Kawa finished with 31 winners against 29 unforced errors and generated 15 break points, converting five. Repeating that level against the world's top-ranked player will be a much tougher challenge, but Kawa has already shown this week that she cannot be overlooked.