Daria Kasatkina

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Jelena Ostapenko, from Latvia, returns a shot to Daria Kasatkina, from Russia, during their finals match at the Volvo Car Open in Charleston, S.C., Sunday, April 9, 2017. Kasatkina won 6-3, 6-1.(AP Photo/Mic Smith)

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Jelena Ostapenko, from Latvia, reacts to a bad shot against Daria Kasatkina, from Russia, during their finals match at the Volvo Car Open in Charleston, S.C., Sunday, April 9, 2017. Kasatkina won 6-3, 6-1.(AP Photo/Mic Smith)

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Daria Kasatkina, from Russia, at right, celebrates with her brother, Alexsandr Kasatkina, center, and coach Vladimir Platenik, left with hand to head, after defeating Jelena Ostapenko, from Latvia, during their finals match at the Volvo Car Open in Charleston, S.C., Sunday, April 9, 2017. Kasatkina won 6-3, 6-1.(AP Photo/Mic Smith)

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Daria Kasatkina, from Russia, celebrates after defeating Jelena Ostapenko, from Latvia, during their finals match at the Volvo Car Open in Charleston, S.C., Sunday, April 9, 2017. Kasatkina won 6-3, 6-1.(AP Photo/Mic Smith)

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Jelena Ostapenko, from Latvia, returns a shot to Daria Kasatkina, from Russia, during their finals match at the Volvo Car Open in Charleston, S.C., Sunday, April 9, 2017. Kasatkina won 6-3, 6-1.(AP Photo/Mic Smith)

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Daria Kasatkina, from Russia, celebrates after defeating Jelena Ostapenko, from Latvia, during their finals match at the Volvo Car Open in Charleston, S.C., Sunday, April 9, 2017. Kasatkina won 6-3, 6-1.(AP Photo/Mic Smith)

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Daria Kasatkina, from Russia, returns a shot to Jelena Ostapenko, from Latvia, during their finals match at the Volvo Car Open in Charleston, S.C., Sunday, April 9, 2017. Kasatkina won 6-3, 6-1.(AP Photo/Mic Smith)

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Serena Williams of the United States eyes the ball as she returns to Daria Kasatkina of Russia during their third round match at the Australian Open tennis championships in Melbourne, Australia, Friday, Jan. 22, 2016.(AP Photo/Aaron Favila)