SAN JOSE, CA - JULY 31: Serena Williams of the United States serves gets ready by her chair before her match against Johanna Konta of Great Britain during Day 2 of the Mubadala Silicon Valley Classic at Spartan Tennis Complex on July 31, 2018 in San Jose, California. (Photo by Ezra Shaw/Getty Images)
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Poppy Harlow to Serena Williams: Thank you
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SAN JOSE, CA - JULY 31: Serena Williams of the United States serves gets ready by her chair before her match against Johanna Konta of Great Britain during Day 2 of the Mubadala Silicon Valley Classic at Spartan Tennis Complex on July 31, 2018 in San Jose, California. (Photo by Ezra Shaw/Getty Images)
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Poppy Harlow to Serena Williams: Thank you
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NEW YORK, NY - SEPTEMBER 08: Serena Williams of the United States reacts after her defeat in the Women's Singles finals match to Naomi Osaka of Japan on Day Thirteen of the 2018 US Open at the USTA Billie Jean King National Tennis Center on September 8, 2018 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Elsa/Getty Images)
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Naomi Osaka, of Japan, holds the trophy after defeating Serena Williams in the women's final of the U.S. Open tennis tournament, Saturday, September 8 in New York.
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Naomi Osaka reacts to controversial win
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Serena Williams argues with the chair umpire during a match against Naomi Osaka, of Japan, during the women's finals of the U.S. Open tennis tournament at the USTA Billie Jean King National Tennis Center, Saturday, Sept. 8, 2018, in New York. (Photo by Greg Allen/Invision/AP)
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NEW YORK, NY - MAY 01: Alexis Ohanian (L) and Serena Williams attend the "Rei Kawakubo/Comme des Garcons: Art Of The In-Between" Costume Institute Gala at Metropolitan Museum of Art on May 1, 2017 in New York City. (Photo by Dimitrios Kambouris/Getty Images)
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MILAN, ITALY - SEPTEMBER 23: Serena Williams is seen leaving the Versace show during Milan Fashion Week Spring/Summer 2017 on September 23, 2016 in Milan, Italy. (Photo by Jacopo Raule/Getty Images)
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Story highlights

Williams opens up on "postpartum emotions"

Says she's been "in a funk"

36-year-old recently suffered heaviest career defeat

CNN  — 

A week after suffering the heaviest defeat of her career, Serena Williams has admitted she is st