Juan Martin del Potro of Argentina returns a shot to against Dominic Thiem of Austria during his fourth round Men's Singles match on Day Eight of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 5, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Al Bello/Getty Images)
US Open: Day 8
Agnieszka Radwanska of Poland returns a shot to Ana Konjuh of Croatia during her fourth round Women's Singles match on Day Eight of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 5, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Al Bello/Getty Images)
US Open: Day 8
Agnieszka Radwanska of Poland hits a return to Ana Konjuh of Croatia during their 2016 US Open women's singles match at the USTA Billie Jean King National Tennis Center on September 5, 2016 in New York. (Photo by Don Emmert/AFP/Getty Images)
US Open: Day 8
Andy Murray of Great Britain hits a return to Grigor Dimitrov of Bulgaria during their 2016 US Open men's singles match at the USTA Billie Jean King National Tennis Center on September 5, 2016 in New York. (Photo by Don Emmert/AFP/Getty Images)
US Open: Day 8
Andy Murray of Great Britain reacts against Grigor Dimitrov of Bulgaria during his fourth round Men's Singles match on Day Eight of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 5, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Al Bello/Getty Images)
US Open: Day 8
A general view of Arthur Ashe Stadium during the fourth round Men's Singles match between Andy Murray of Great Britain and Grigor Dimitrov of Bulgaria on Day Eight of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 5, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Al Bello/Getty Images)
US Open: Day 8
Andy Murray of Great Britain hits a return to Grigor Dimitrov of Bulgaria during their 2016 US Open men's singles match at the USTA Billie Jean King National Tennis Center on September 5, 2016 in New York. (Photo by Don Emmert/AFP/Getty Images)
US Open: Day 8
Kei Nishikori of Japan returns a shot to Ivo Karlovic of Croatia during his fourth round Men's Singles match on Day Eight of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 5, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Michael Reaves/Getty Images)
US Open: Day 8
Ivo Karlovic of Croatia serves to Kei Nishikori of Japan during his fourth round Men's Singles match on Day Eight of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 5, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Michael Reaves/Getty Images)
US Open: Day 8
Serena Williams of the United States serves against Yaroslava Shvedova of Kazakhstan during her fourth round Women's Singles match on Day Eight of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 5, 2016 in the Queens borough of New York City. (Photo by Chris Trotman/Getty Images for USTA)
US Open: Day 8
Serena Williams of the United States signs her autograph for fans after defeating Yaroslava Shvedova of Kazakhstan during her fourth round Women's Singles match on Day Eight of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 5, 2016 in the Queens borough of New York City. (Photo by Chris Trotman/Getty Images for USTA)
US Open: Day 8
Yaroslava Shvedova of Kazakhstan returns a shot to Serena Williams of the United States during her fourth round Women's Singles match on Day Eight of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 5, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Al Bello/Getty Images)
US Open: Day 8
Yaroslava Shvedova of Kazakhstan hits a return against Serena Williams of US during their 2016 US Open Women's Singles match at the USTA Billie Jean King National Tennis Center in New York on September 5, 2016. (Photo by Eduardo Munoz Alvarez/AFP/ Getty Images)
Anna Wintour At US Open
Anna Wintour watches the fourth round Women's Singles match between Venus Williams of the United States and Karolina Pliskova of the Czech Republic on Day Eight of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 5, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Mike Hewitt/Getty Images)
US Open: Day 8
Serena Williams of the United States celebrates her win over Yaroslava Shvedova of Kazakhstan during her fourth round Women's Singles match on Day Eight of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 5, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Mike Hewitt/Getty Images)
US Open: Day 8
Serena Williams of the United States returns a shot to Yaroslava Shvedova of Kazakhstan during her fourth round Women's Singles match on Day Eight of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 5, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Al Bello/Getty Images)
US Open: Day 8
Stan Wawrinka of Switzerland celebrates his win against Illya Marchenko of Ukraine during his fourth round Men's Singles match on Day Eight of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 5, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Michael Reaves/Getty Images)
2016 US Open - Day 8
Karolina Pliskova of the Czech Republic reacts after her win over Venus Williams of the United States during her fourth round Women's Singles match on Day Eight of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 5, 2016 in the Queens borough of New York City. (Photo by Chris Trotman/Getty Images for USTA)
2016 US Open - Day 8
Karolina Pliskova of the Czech Republic returns a shot to Venus Williams of the United States during her fourth round Women's Singles match on Day Eight of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 5, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Mike Hewitt/Getty Images)
US Open: Day 8
Venus Williams of United States reacts as she plays against Karolina Pliskova of Czech Republic during their 2016 US Open Women's Singles match at the USTA Billie Jean King National Tennis Center in New York on September 5, 2016. (Photo by Kena Betancur/AFP/Getty Images)
2016 US Open - Day 8
Illya Marchenko of Ukraine reacts against Stan Wawrinka of Switzerland during his fourth round Men's Singles match on Day Eight of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 5, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Michael Reaves/Getty Images)
US Open: Day 8
Venus Williams of US hits a return against Karolina Pliskova of the Czech Republic during their 2016 US Open Women's Singles match at the USTA Billie Jean King National Tennis Center in New York on September 5, 2016. (Photo by Eduardo Munoz Alvarez/AFP/ Getty Images)
US Open: Day 8
Karolina Pliskova of the Czech Republic shakes hands after her win over Venus Williams of the United States during her fourth round Women's Singles match on Day Eight of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 5, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Al Bello/Getty Images)
US Open: Day 8
Stan Wawrinka of Switzerland hits a return against Illya Marchenko of the Ukraine during their 2016 US Open Men's Singles match at the USTA Billie Jean King National Tennis Center in New York on September 5, 2016. (Photo by Jewel Samad/AFP/Getty Images)
US Open: Day 8
Juan Martín del Potro of Argentina signs his autograph for fans on Day Eight of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 5, 2016 in the Queens borough of New York City. (Photo by Chris Trotman/Getty Images for USTA)
US Open: Day 8
Carla Suarez Navarro of Spain returns a shot to Simona Halep of Romania during her fourth round Women's Singles match on Day Eight of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 5, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Michael Reaves/Getty Images)
US Open: Day 8
Simona Halep of Romania returns a shot to Carla Suarez Navarro of Spain during her fourth round Women's Singles match on Day Eight of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 5, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Michael Reaves/Getty Images)
US Open: Day 8
Simona Halep of Romania reacts after defeating Carla Suarez Navarro of Spain during her fourth round Women's Singles match on Day Eight of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 5, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Michael Reaves/Getty Images)
US Open: Day 8
Juan Martin del Potro of Argentina celebrates his victory after Dominic Thiem of Austria retired during their 2016 US Open Men's Singles match at the USTA Billie Jean King National Tennis Center in New York on September 5, 2016. (Photo by Eduardo Munoz Alvarez/AFP/ Getty Images)
