LONDON - China's Olympic champion Zheng Qinwen fought hard to reach the quarterfinals of the women's singles at the Queen's Club Championships on Thursday.

The 22-year-old Zheng, ranked world No. 5, needed two hours and 11 minutes to overcome McCartney Kessler of the United States 6-3, 4-6, 7-5 in the second round.

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Zheng entered the WTA 500 tournament as the top seed and received a bye in the first round. She said she didn't expect her first match on grass this season to be easy - and she was indeed tested Thursday evening.

Zheng admitted she lost focus briefly after taking the opening set and struggled to adjust in time.

World No. 42 Kessler broke in the 10th game of the second set to even the match and then broke first in the decider, but a composed Zheng fought back to seal the win.

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"I believe I should play even more aggressive on the grass court, but I need to be patient at the same time. I need to find the balance," said Zheng after the match.

The Paris Olympic champion will next face British wild card Emma Raducanu on Friday. Raducanu, a former US Open champion, advanced by defeating Rebecca Sramkova of Slovakia 6-4, 6-1.

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"As a British player, she definitely has more experience on the grass court," Zheng said. "But I will pull out all the stops tomorrow. I will try my best to focus on every point."

Former Wimbledon champion Elena Rybakina also secured a quarterfinal berth by defeating Britain's Heather Watson 6-4, 6-2.

The fourth-seeded Kazakh will face German veteran Tatjana Maria on Friday.