She partnered Li Ju to victory in Sydney four years ago, while Zhang, 22, the world singles number one, was making her Olympic debut.

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Ms Li said she had resorted to keeping a basin of water in the house in the hope it might act as an air purifier.

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In the tiebreak, Williams was struggling until nerves got the better of Li as she made a series of unforced errors and the top seed took advantage to close it out with a second-service ace after 58 minutes.

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