In Photos: Day 4 of the U.S. Open tennis championship
Andy Murray cools off with ice wrapped around his neck between gamesCharles Krupa/The Associated Press
Jack Sock of the United States receives assistance or heat exhaustionGetty Images
Andy Murray of Britain runs down a return to Adrian MannarinoAdrees Latif/Reuters
Simona Halep of Romania hits a return to Kateryna BondarenkoCarlo Allegri/Reuters
Andy Murray of Great Britain serves to Adrian MannarinoRobert Deutsch
Ruben Bemelmans of Belgium returns to Jack SockJewel Samad/Getty Images
Simona Halep of Romania plays against Kateryna BondarenkoTimothy A Clary/Getty Images
Thomaz Bellucci of Brazil serves to Yoshihito NishiokaJerry Lai
Jelena Ostapenko of Latvia serves to Sara ErraniAl Bello/Getty Images
Hyeon Chung of South Korea returns to Stan WawrinkaJewel Samad/Getty Images
Sara Errani of Italy serves to Jelena OstapenkoAl Bello/Getty Images
Angelique Kerber of Germany returns a shot against Karin KnappStreeter Lecka/Getty Images
Jelena Ostapenko of Latvia returns a shot to Sara ErraniAl Bello/Getty Images
Victoria Azarenka of Belarus returns a shot to Yanina WickmayerCharles Krupa/The Associated Press
Andrea Petkovic of Germany serves to Elena VesninaJerry Lai
Garbine Muguruza of Spain returns a shot to Johanna KontaMatthew Stockman/Getty Images
Victoria Azarenka of BelarusCharles Krupa/The Associated Press
Yanina Wickmayer of Belgium servesCharles Krupa/The Associated Press