The US Open quarter-final between Novak Djokovic and John Millman ground to an astonishing halt at 2-2 in the second set Wednesday when the umpire gave Millman permission to leave the court to change his sweat-soaked clothes.

A break in play of six and a half minutes saw 13-time Grand Slam champion Djokovic remain on the court as Australia's Millman -- who apologized profusely to Djokovic -- disappeared.

"I could do with a rest," said Djokovic, who also used the break to send a ballboy over to his box in the stands seeking to get some tablets he thought his wife had brought to the tournament for him.

When play resumed, Millman held serve for a 3-2 lead in the second set -- then they both sat down for the changeover.

Millman, ranked 55th in the world and playing in his first Grand Slam quarter-final, admitted that when he asked the umpire if he could leave to change, he didn't know what the rule was.

The US Tennis Association issued a statement on the incident, saying the umpire deemed the situation to be within the "Equipment Out of Adjustment" provision -- and the moisture dripping from his clothes was hazardous enough to warrant the break.

A similar situation occurred between the fourth and fifth sets of Rafael Nadal's victory over Dominic Thiem on Tuesday, when Thiem was allowed to retrieve dry shoes from the locker room, which extended the normal amount of time between sets.

Djokovic said the fierce humidity that has prevailed throughout the tournament had made competing a sweatier affair than he'd ever seen.

"Incredible," said Djokovic, who emerged a 6-3, 6-4, 6-4 winner over Millman in a match featuring an array of entertaining but physically draining rallies. "I have to take 10 shirts every match."

Djokovic added later that the tournament needs to address the problem of air circulation on the Arthur Ashe Stadium.