New York - Weather reigned again as the hot topic at the US Open on Tuesday, a day after Roger Federer's hopes of a sixth title melted away in a shock loss to 55th-ranked John Millman.
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The Swiss superstar, owner of 20 Grand Slam titles, said the suffocating humidity on Arthur Ashe Stadium played a role in the defeat.
"I felt I couldn't get air," Federer said. "There was no circulation at all. It's one of the first times it's happened to me ... (you) just keep on sweating more and more and more and more as the match goes on."
There was to be no relief on Tuesday, with a heat advisory issued by the National Weather Service thanks to expected temperatures of around 34 C and humidity of 60 percent.
Federer said he thought such conditions had become more problematic on Ashe since the addition of the retractable roof led to diminished airflow in the 23,000-seat stadium.
But players have suffered on all courts -- five retiring from heat-related problems in the first round to prompt organizers to implement an extreme heat policy allowing a 10 minute break in both men's and women's matches that go beyond straight sets.
It's the first time in Grand Slam history that such a break has been offered to the men.
The break proved less useful in week one to players toiling on outside courts -- far away from the sanctuary of a locker room.
But it could be a boon to players fighting Tuesday for semi-final berths on Ashe, including defending champions Rafael Nadal and Sloane Stephens and former champions Serena Williams and Juan Martin del Potro.