Serena Williams of the United States serves to Vania King of the United States during her second round Women's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Elsa/Getty Images)
US Open: Day 4
Elena Vesnina of Russia serves to Annika Beck of Germany during her second round Women's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Michael Reaves/Getty Images)
US Open: Day 4
Dominic Thiem of Austria returns a shot to Ricardas Berankis of Lithuana during his second round Men's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Michael Reaves/Getty Images)
US Open: Day 4
Vania King of the United States reacts against Serena Williams of the United States during her second round Women's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Elsa/Getty Images)
2016 US Open - Day 4
Serena Williams of the United States reacts against Vania King of the United States during her second round Women's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Elsa/Getty Images)
Jay-Z And Beyonce At US Open
Jay-Z and Beyonce watch the second round Women's Singles match between Serena Williams of the United States and Vania King of the United States on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Al Bello/Getty Images)
Beyonce At US Open
Singer Beyoncé watches the match between Serena Williams of the US Vania King of the US during their 2016 US Open women's singles match at the USTA Billie Jean King National Tennis Center on September 1, 2016 in New York. (Photo by Don Emmert/AFP/Getty Images)
US Open: Day 4
Viktor Troicki of Serbia returns a shot against Jared Donaldson of the United States in their second round Men's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Queens borough of New York City. (Photo by Mike Stobe/Getty Images for USTA)
US Open: Day 4
Annika Beck of Germany returns a shot to Elena Vesnina of Russia during her second round Women's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Michael Reaves/Getty Images)
US Open: Day 4
Serena Williams of the United States acknowledges the crowd after defeating Vania King of the United States during her second round Women's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Elsa/Getty Images)
US Open: Day 4
Caroline Garcia of France celebrates her victory over Katerina Siniakova of the Czech Republic during her second round Women's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Alex Goodlett/Getty Images)
US Open: Day 4
Agnieszka Radwanska of Poland returns a shot to Naomi Broady of the United Kingdom during her second round Women's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Alex Goodlett/Getty Images)
US Open: Day 4
Anastasia Pavlyuchenkova of Russia celebrates her win over Kristina Mladenovic of France during her second round Women's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Mike Hewitt/Getty Images)
US Open: Day 4
Katerina Siniakova of the Czech Republic returns a shot to Caroline Garcia of France during her second round Women's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Alex Goodlett/Getty Images)
US Open: Day 4
Steve Johnson of the United States reacts against Juan Martin del Potro of Argentina during his second round Men's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Al Bello/Getty Images)
US Open: Day 4
Alessandro Giannessi of Italy returns a shot to Stan Wawrinka of Switzerland during his second round Men's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Alex Goodlett/Getty Images)
US Open: Day 4
Laura Siegemund of Germany returns a shot to Nicole Gibbs of the United States during her second round Women's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Andy Lyons/Getty Images)
US Open: Day 4
Grigor Dimitrov of Bulgaria returns a shot to Jeremy Chardy of France during his second round Men's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Michael Reaves/Getty Images)
US Open: Day 4
Donald Young of the United States returns a shot to Ivo Karlovic of Croatia during his second round Men's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Elsa/Getty Images)
US Open: Day 4
Juan Martin del Potro of Argentina reacts after defeating Steve Johnson of the United States during his second round Men's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Elsa/Getty Images)
US Open: Day 4
Stan Wawrinka of Switzerland returns a shot to Alessandro Giannessi of Italy during his second round Men's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Alex Goodlett/Getty Images)
US Open: Day 4
Jelena Jankovic of Serbia returns a shot to Carla Suarez Navarro of Spain during her second round Women's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Alex Goodlett/Getty Images)
US Open: Day 4
Juan Martin del Potro of Argentina falls on the court during his match with Steve Johnson of the US during their 2016 US Open men's singles match at the USTA Billie Jean King National Tennis Center on September 1, 2016 in New York. (Photo by Don Emmert/AFP/Getty Images)
US Open: Day 4
Juan Martin del Potro of Argentina plays the shot in between his legs to Steve Johnson of the United States during his second round Men's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Al Bello/Getty Images)
US Open: Day 4
Steve Johnson of the United States returns a shot to Juan Martin del Potro of Argentina during his second round Men's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Al Bello/Getty Images)
US Open: Day 4
Fabio Fognini of Italy returns a shot to David Ferrer of Spain during his second round Men's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Elsa/Getty Images)
US Open: Day 4
Alexander Zverev of Germany reacts against Daniel Evans of Great Britain during his second round Men's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Michael Reaves/Getty Images)
US Open: Day 4
Venus Williams of the United States reacts against Julia Goerges of Germany during her second round Women's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Al Bello/Getty Images)
US Open: Day 4
Venus Williams of the United States serves to Julia Goerges of Germany during her second round Women's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Al Bello/Getty Images)
US Open: Day 4
Venus Williams of the United States returns a shot to Julia Goerges of Germany during her second round Women's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Al Bello/Getty Images)
US Open: Day 4
Andy Murray of Great Britain celebrates his victory over Marcel Granollers of Spain during his second round Men's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Al Bello/Getty Images)
US Open: Day 4
Kurumi Nara of Japan serves to Ana Konjuh of Croatia during her second round Women's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Elsa/Getty Images)
US Open: Day 4
Karolina Pliskova of the Czech Republic returns a shot to Montserrat Gonzalez of Paraguay during her second round Women's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Michael Reaves/Getty Images)
US Open: Day 4
Andy Murray of Great Britain returns a shot to Marcel Granollers of Spain during his second round Men's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Al Bello/Getty Images)
US Open: Day 4
Simona Halep of Romania returns a shot to Lucie Safarova of the Czech Republic during her second round Women's Singles match on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Al Bello/Getty Images)
