Five athletes were forced to retire from the opening round of the US Open due to heat-related issues.
Temperatures close to 38C (100F) were recorded in New York. The heat was made more stifling by humidity levels of over 50%.
Six players were forced to retire from matches on Tuesday, with the United States Tennis Association (USTA) saying five of the withdrawals - Italian qualifier Stefano Travaglia, Lithuanian Ricardas Berankis, Argentine Leonardo Mayer, Russia's Mikhail Youzhny and Serb Filip Krajinovic - were "heat-related".