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SINGAPORE - OCTOBER 27: Madison Keys of the United States plays a forehand in her singles match against Angelique Kerber of Germany during day 5 of the BNP Paribas WTA Finals Singapore at Singapore Sports Hub on October 27, 2016 in Singapore. (Photo by Clive Brunskill/Getty Images)

SINGAPORE - OCTOBER 27: Madison Keys of the United States plays a forehand in her singles match against Angelique Kerber of Germany during day 5 of the BNP Paribas WTA Finals Singapore at Singapore Sports Hub on October 27, 2016 in Singapore.  (Photo by Clive Brunskill/Getty Images)