Novak Djokovic believes that the man who lifts the US Open trophy on Sunday will have truly earned the mantle of champion, describing the hot and steamy 2018 tournament as the "toughest" he has encountered.
Djokovic, the winner in 2011 and 2015, faces Kei Nishikori in Friday's semi-finals, his 11th successive appearance in the last-four.
An eighth final is within reach and to achieve that, the 31-year-old expects Nishikori to make him sweat -- literally.
"From my experience, and I can only talk about myself, this has been definitely the toughest US Open in the last ten years that I have played in in terms of conditions," said the 13-time major winner.
The US Open has been played out in sweltering temperatures -- over the 30-degree mark most days -- and crushing humidity.
Roger Federer was drenched through after his shock fourth round loss to world number 55 John Millman, complaining it was impossible to breathe down in the cavernous Arthur Ashe Stadium.
Djokovic said he changed his shirt 10 times in his quarter-final victory over Millman in a match which was held up for more than six minutes at 2-2 in the second set when the Australian left the court to change his clothes.
"It's OK," Djokovic told Millman. "I need a rest."
Djokovic admitted this event could be ranked "as the sweatiest Slam ever".
"I personally have never sweated as much as I have here. Incredible. I mean, I have to take at least 10 shirts for every match. It's literally after two games you're soaking."
Federer, 37, had speculated that since the roof and its supports were built over the Ashe stadium, there has been an decrease in the air flow.
Djokovic said the tournament needs to address the problem of air-conditioning in an arena which can hold almost 25,000 people.
- Like a sauna -
"I asked the chair umpire whether they are using some form of ventilation or air conditioning down at the court level side, and he said he's not aware of it -- it's only what comes through the hallway," added Djokovic.
"It's fantastic to have the roof but it feels like a sauna."
Fortunately for Djokovic, as well as Nishikori and Rafael Nadal and Juan Martin del Potro, who meet in the other semi-final, Friday is expected to be a more comfortable 24 degrees.
Djokovic, rejuvenated by a fourth Wimbledon title after a spell of struggles with form and confidence since wrapping up the career Grand Slam in Paris in 2016, enjoys an equally comfortable record over Japan star Nishikori.
He leads their head-to-head 14-2, including all three meetings in 2018, the latest of which was at Wimbledon in the quarter-finals.
He has won the last 13 although Nishikori defeated the Serb in New York in the 2014 semi-finals on his way to a runners-up spot against Marin Cilic.
"I can't really say he's a great matchup for me," said Djokovic.
"He plays so fast, he makes me more alert from the first point, because I know I have to be at my best in order to compete with him from the baseline."