Roger Federer was left disappointed after a shock defeat to unseeded Australian John Millman in the round of 16 of the US Open on Monday.Federer struggled to deal with the heat at Flushing Meadows and a relentless Millman didn’t help his cause as the 20-time Grand Slam champion suffered a 6-3 5-7 6-7(7) 6-7(3) loss to the Australian despite being a set up.This was just the fifth time since 2004 that Federer has exited a Grand Slam before the quarter-final and the suffocating humidity did expose Federer’s age as he looked every bit of a 37-year-old.”I just thought it was very hot tonight,” Federer said after his fourth-round defeat. It was just one of those nights where I guess I felt I couldn’t get air. There was no circulation at all. I don’t know, for some reason I just struggled in the conditions tonight.”It’s one of the first times it’s happened to me. When you feel like that, everything is off. But, look, I’ve trained in tougher conditions. I’ve played in the daytime, you know, at 120 (degrees Fahrenheit, 49 Celsius). Some days it’s just not the day where the body can cope with it,” Federer said after his loss to Millman.Also read – Roger Federer loses to John Millman in last 16, Djokovic in quartersFederer’s numbers in the match are disastrous. Federer, seeded second, committed 77 unforced errors and made 10 double faults, including two in the final tie-break. Roger Federer lost the match despite winning the first set (AP Photo)Millman on the other hand, didn’t want to let the opportunity of pulling off the biggest upset of his career so far pass. Ranked 55 in the world, Millman had never beaten a top 10 player and never before at the US Open had Federer lost to someone ranked outside the top 50, previously posting a 40-0 record in such matches at Flushing Meadows.advertisementBut, both the records came crumbling down as the Arthur Ashe Stadium stood stunned after the five-time champion made his earliest departure from the year’s final Grand Slam since a fourth-round loss to Tommy Robredo in 2013.Federer’s incredible comeback after a drab 2016 had made everybody stand up and applaud the great. People, who had been picking on him for faults were left red faced but come September 4, signs of decay finally showed on a sweltering day in New York City.However, there was no surrender – he wrestled with Millman through two tie-breaks – but in the end Federer simply ran out of steam and ideas.Gracious and classy as always.Until next time, @rogerfederer…#USOpen pic.twitter.com/zxPLUSbFuDUS Open Tennis (@usopen) September 4, 2018While Federer suffered in the oppressive conditions, at the other end of court 29-year-old Millman, who lives and trains in the heat and humidity of Brisbane, looked perfectly at home.”John was able to deal with it better. He maybe comes from one of the most humid places on earth, Brisbane. I knew I was in for a tough one. Maybe when you feel like that, as well, you start missing chances and I had those,” said Federer.