Cilic reaches second round after Copil retires hurt

Cilic, who was champion in 2014, was cruising against Copil, who quit with a left-arm strain, according to a USTA official.

The match took place in heat and humidity, as temperatures climbed above 90 degrees Fahrenheit (30 degrees Celsius), battering players across Flushing Meadows.

Seventh seed Cilic, who said it was “one of the most brutal days that we had so far this year,” told reporters the heat, plus the pressure of the shot clock introduced at the tournament this year, had proved challenging.

“I was just missing some easy balls, making some unforced errors that are not that usual for me,” Cilic said, referring to his performance early in the match. “Conditions definitely were extremely tough and very humid, very hot.”