Raducanu stunned the sporting world last year when she went from qualifier to winner of the women's singles in an incredible fortnight in New York. But she came unstuck against Cornet, who was playing in her 63rd straight Grand Slam. Cornet defeated Raducanu 6-3, 6-3 in 1 hour, 42 minutes.
"I'm obviously disappointed to lose first round," Raducanu said. "Yeah, I mean, credit to Alize, she played pretty well. I mean [it is] obviously really disappointing, [I'm] really sad to leave here. It's probably my favorite tournament.
"But also, I mean, in a way [I'm] happy because it's a clean slate. I'm going to drop down the rankings. Climb my way back up."
It was a match in which both players struggled to hold serve in blustery conditions in Louis Armstrong Stadium, and there were five breaks of serve in the first set.
"I think it was quite windy," Raducanu said. "It was blowing, like, from back-to-front. It was quite difficult for me especially to find my ball toss. I think I was hitting quite a lot of serves long. I just struggled to adapt to it really.
"And, I mean, it's something that both players have to kind of deal with. She just dealt with it better than me today."
Raducanu called a medical timeout at the end of the first set for treatment on her right hand, having suffered from blisters there during her practice session on Friday.
"I got a new one," Raducanu said. "But, like, you know, you tape it up and move on it. It's a blister. Not much you can do about it."
Cornet and Raducanu exchanged breaks at the start of the second set but the key spell came in the seventh game, when Cornet broke Raducanu's serve to go up 4-3. She held in the eighth and needed just one match point to break Raducanu again and progress to the second round.
The victory is another highlight in Cornet's year, after she reached the quarterfinals of the Australian Open and defeated world No.1 Iga Swiatek at Wimbledon.
For Raducanu, the defeat will see her fall in the WTA rankings as she loses 2030 points she won here last year. This is her first full year on the WTA Tour. She lost in the second round at the Australian Open, Roland Garros and Wimbledon ahead of this first-round exit at Flushing Meadows.
"This one obviously hurts a bit because it's my favorite tournament and obviously like a lot of emotions in the past year," she said.
"Yeah, I mean, I'm proud for putting myself out there every match, every day. Like I know I'm pushing myself to be the best I can."
She added: "I mean, in a way the target will be off my back slightly. Yeah, I just have another chance to claw my way back up there."
Raducanu is unsure of what her next steps will be and which tournaments she'll play in for the rest of the year. She was also noncommittal on whether she'll continue working with coach Dmitry Tursunov, who's been with her for the past six weeks.
She feels her main focus of improvement is to get a better consistency over the course of next year.
"If I look at how much tennis I played this year, or training I've done, it's very, very minimal," she said.
"We, like, actually counted the days.
"From, like, Rome to a bit after Wimbledon, I only played tennis for, like, 14 days in two months and a half or something. It was pretty wild.
"I think the most important thing for me is just consistency of these weeks, of training, of competing. You lose a match, you're on the practice court like two days later or something. It's just not having these big chunks of gaps."