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STANFORD, CA - JULY 19: Elitsa Kostova of Bulgaria competes against Sachia Vickery of the United States during day two of the Bank of the West Classic at the Stanford University Taube Family Tennis Stadium on July 19, 2016 in Stanford, California. (Photo by Lachlan Cunningham/Getty Images)

STANFORD, CA - JULY 19: Elitsa Kostova of Bulgaria competes against Sachia Vickery of the United States during day two of the Bank of the West Classic at the Stanford University Taube Family Tennis Stadium on July 19, 2016 in Stanford, California. (Photo by Lachlan Cunningham/Getty Images)