Former champion Juan Martin del Potro reached the US Open semi-finals with a 6-7 (5-7) 6-3 7-6 (7-4) 6-2 win over John Isner on another gruelling day.
The humidity was so stifling officials suspended junior matches on outside courts for more than two hours.
Del Potro and Isner had a 10-minute break between the third and fourth sets as part of the extreme heat policy.
Del Potro joked: “I had a shower, re-taped my ankles and laid down on the table. I didn’t want to come back out.”
Isner said he got through 11 shirts and estimated he lost between eight and 10 pounds through sweating as temperatures approached 38C inside Arthur Ashe Stadium.
“It’s tough conditions out there, no doubt,” said the American. “It’s very humid. The air is pretty still for whatever reason. Maybe it’s the roof structure.”