NINGBO, China -- Top-ranked Elena Rybakina advanced to the Ningbo Open quarterfinals after Polina Kudermetova retired with a midmatch injury when trailing 5-0 on Thursday.

Rybakina is the defending champion at the hard-court event in China and will next play Katarzyna Kawa, who defeated No. 5-seeded Belinda Bencic 7-5, 6-2.

Kudermetova called for the physio at 3-0 and attempted to continue in the second-round match before opting to stop. She was emotional as she left the court.

"I think Polina, before, she played some tough matches and conditions here are not easy," Rybakina said. "The balls are quite heavy. I just wish her a speedy recovery and hope it's nothing too serious."

Alex Eala of the Philippines survived six match points before losing 7-5, 6-4 to sixth-seeded Diana Shnaider, who reached the quarterfinals in Ningbo for the third time in four appearances.