BEIJING -- World No.6 Coco Gauff advanced to her consecutive China Open quarterfinal after Naomi Osaka retired with injury. Osaka won the opening set 6-3 and led by a break in the second set before Gauff came back from 4-3 down to win the last three games of the set before Osaka retired due to a lower back injury at 3-6, 6-4.

Beijing: Scores | Order of Play | Draws

"I wasn't sure if it was her hip or back, I just knew that towards the end she could barely jump on her serve," Gauff said, "so I knew that it was something that, in the moment, was probably bad but hopefully it's something that's not a long-term thing."

With the win, Gauff edged ahead in the head-to-head to lead Osaka 3-2. All five meetings have come on hard court.

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Entering the match, Osaka was bidding to capture her fourth consecutive match win for the first time since her comeback from maternity leave. After an exchange of service breaks to open the match, Osaka extended her lead to 3-1 after a pair of baseline errors from Gauff. 

But after getting broken for a second time, Osaka called the trainer for a short chat on the 3-2 changeover. Osaka looked cautious with her movement for the next two games, and took advantage of Gauff's more error-prone play to earn a third break before serving out the set. 

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Gauff broke to build a 2-0 lead in the second set but Osaka coolly clawed her way back. With Gauff serving at 3-3, 30-30, Osaka benefitted from the American's sixth double fault of the night and broke to lead 4-3. But Osaka struck her first double fault of the match on break point to hand back her advantage and Gauff held at love to lead 5-4.

With Osaka struggling to land her first serves, Gauff pounced, breaking the four-time major champion to take the second set. Osaka promptly retired, greeting Gauff with a hug and an apology.

"Towards the end of the second set, I really saw it was hampering her movement a lot," Gauff said. "Even if you saw that last point, I was just trying to keep the ball in because I knew what was going on. But I didn't expect her to retire at that moment, honestly.

"I just told her she should be proud of herself. It's not easy. I think this is her first time winning three matches in a tournament [for a while]. So physically, you can do all the running you want but match-fit is different. Hopefully, she'll be fine. I think she's signed up for Wuhan."

A semifinalist in her tournament debut last year, Gauff will next face Ukrainian qualifier Yuliia Starodubtseva for a spot in her first semifinal since Berlin.

Gauff is playing her first tournament after adding Matt Daly to her team and she has been vocal about her intention to use the end of the season to work on her serve and baseline aggression. Her commitment to the process has meant playing against her base instincts, resulting in more error spells, but the 20-year-old has her eyes trained fully forward. 

"I'm not focused on results at all at this point in the season," Gauff said. "It's one of those sacrifices. It's great to be in the quarters, I probably didn't expect it to be honest. But it's one of those things where you sacrifice to get better in the long term. I'm treating this tournament as practice and everything is a plus."