2019 US Open

Donna Vekic of Croatia serves during her Women's Singles second round match against Kaia Kanepi of Estonia on day four of the 2019 US Open at the USTA Billie Jean King National Tennis Center on August 29, 2019 in Queens borough of New York City. (Photo by Emilee Chin/Getty Images)

2019 US Open - Day 4

Cori Gauff of the United States returns a shot during her Women's Singles second round match against Timea Babos of Hungary on day four of the 2019 US Open at the USTA Billie Jean King National Tennis Center on August 29, 2019 in Queens borough of New York City. (Photo by Emilee Chinn/Getty Images)

2019 US Open - Day 4

Cori Gauff of the United States returns a shot during her Women's Singles second round match against Timea Babos of Hungary on day four of the 2019 US Open at the USTA Billie Jean King National Tennis Center on August 29, 2019 in Queens borough of New York City. (Photo by Emilee Chinn/Getty Images)

2019 US Open - Day 4

Cori Gauff of the United States celebrates victory during her Women's Singles second round match against Timea Babos of Hungary on day four of the 2019 US Open at the USTA Billie Jean King National Tennis Center on August 29, 2019 in Queens borough of New York City. (Photo by Emilee Chinn/Getty Images)

2019 US Open - Day 4

Cori Gauff of the United States celebrates victory during her Women's Singles second round match against Timea Babos of Hungary on day four of the 2019 US Open at the USTA Billie Jean King National Tennis Center on August 29, 2019 in Queens borough of New York City. (Photo by Emilee Chin/Getty Images)

2019 US Open - Day 4

Cori Gauff of the United States and Timea Babos of Hungary shake hands follwing their Women's Singles second round match on day four of the 2019 US Open at the USTA Billie Jean King National Tennis Center on August 29, 2019 in Queens borough of New York City. (Photo by Matthew Stockman/Getty Images)

2019 US Open - Day 4

Andrea Petkovic of Germany returns a shot during her Women's Singles second round match against Petra Kvitova of the Czech Republic on day four of the 2019 US Open at the USTA Billie Jean King National Tennis Center on August 29, 2019 in Queens borough of New York City. (Photo by Mike Stobe/Getty Images for USTA)

2019 US Open - Day 4

Andrea Petkovic of Germany serves the ball during her Women's Singles second round match against Petra Kvitova of the Czech Republic on day four of the 2019 US Open at the USTA Billie Jean King National Tennis Center on August 29, 2019 in Queens borough of New York City. (Photo by Mike Stobe/Getty Images for USTA)

2019 US Open - Day 4

Caroline Wozniacki of Denmark returns a shot during her Women's Singles second round match against Danielle Collins of the United States on day four of the 2019 US Open at the USTA Billie Jean King National Tennis Center on August 29, 2019 in Queens borough of New York City. (Photo by Steven Ryan/Getty Images)

2019 US Open - Day 4

Caroline Wozniacki of Denmark shakes hands with Danielle Collins of the United States after defeating her in their Women's Singles second round match on day four of the 2019 US Open at the USTA Billie Jean King National Tennis Center on August 29, 2019 in Queens borough of New York City. (Photo by Steven Ryan/Getty Images)

2019 US Open - Day 4

Donna Vekic of Croatia returns a shot during her Women's Singles second round match against Kaia Kanepi of Estonia on day four of the 2019 US Open at the USTA Billie Jean King National Tennis Center on August 29, 2019 in Queens borough of New York City. (Photo by Clive Brunskill/Getty Images)

2019 US Open - Day 4

Taylor Townsend of the United States returns a shot during her Women's Singles second round match against Simona Halep of Romania on day four of the 2019 US Open at the USTA Billie Jean King National Tennis Center on August 29, 2019 in Queens borough of New York City. (Photo by Elsa/Getty Images)

2019 US Open - Day 4

Simona Halep of Romania and Taylor Townsend of the United States shake hands following their Women's Singles second round match on day four of the 2019 US Open at the USTA Billie Jean King National Tennis Center on August 29, 2019 in Queens borough of New York City. (Photo by Elsa/Getty Images)

2019 US Open - Day 4

Taylor Townsend of the United States celebrates victory during her Women's Singles second round match against Simona Halep of Romania on day four of the 2019 US Open at the USTA Billie Jean King National Tennis Center on August 29, 2019 in Queens borough of New York City. (Photo by Elsa/Getty Images)

2019 US Open - Day 4

Taylor Townsend of the United States celebrates victory during her Women's Singles second round match against Simona Halep of Romania on day four of the 2019 US Open at the USTA Billie Jean King National Tennis Center on August 29, 2019 in Queens borough of New York City. (Photo by Elsa/Getty Images)

2019 US Open - Day 4

John Isner of the United States returns a shot during his Men's Singles second round match against Jan-Lennard Struff of Germany on day four of the 2019 US Open at the USTA Billie Jean King National Tennis Center on August 29, 2019 in Queens borough of New York City. (Photo by Al Bello/Getty Images)

2019 US Open - Day 4

Frances Tiafoe of the United States returns a shot during his Men's Singles second round match against Alexander Zverev of Germany on day four of the 2019 US Open at the USTA Billie Jean King National Tennis Center on August 29, 2019 in Queens borough of New York City. (Photo by Elsa/Getty Images)

2019 US Open - Day 4

Naomi Osaka of Japan returns a shot during her Women's Singles second round match against Magda Linette of Poland on day four of the 2019 US Open at the USTA Billie Jean King National Tennis Center on August 29, 2019 in Queens borough of New York City. (Photo by Al Bello/Getty Images)

2019 US Open - Day 4

Naomi Osaka of Japan returns a shot during her Women's Singles second round match against Magda Linette of Poland on day four of the 2019 US Open at the USTA Billie Jean King National Tennis Center on August 29, 2019 in Queens borough of New York City. (Photo by Al Bello/Getty Images)

2019 US Open - Day 4

Naomi Osaka of Japan celebrates victory following her Women's Singles second round match against Magda Linette of Poland on day four of the 2019 US Open at the USTA Billie Jean King National Tennis Center on August 29, 2019 in Queens borough of New York City. (Photo by Al Bello/Getty Images)