Raducanu, 18, got the better of the 19-year-old Canadian at Flushing Meadows to win in stunning fashion in the first episode of what promises to be a long-lasting rivalry.
The Briton has enjoyed the highs of star-studded red-carpet events since her New York win, but she suffered a disappointing 6-2 6-4 loss to Aliaksandra Sasnovich.
It was just her third WTA Tour tournament and she is not going to beat herself up at the loss.
“I think it’s going to take me time to adjust really to what’s going on,” she said. “I mean, I’m still so new to everything.
“Like the experiences that I’m going through right now, even though I might not feel 100 per cent amazing right now, I know they’re for the greater good.
“For the bigger picture, I’ll be thanking this moment. So, that’s the lesson I think, that you can easily get sucked into being so focused on the result and getting disappointed.
“I mean, I’m 18 years old. I need to cut myself some slack.
“I’m still very, very new to the tour. I think that experience just comes from playing week in, week out and experiencing all these different things.”
Fernandez enjoyed her return much more, beating Alize Cornet 6-2 6-3.
She said: “I am very happy with the way I played. I trained very hard after the final.
“I just come out to enjoy myself and see where the results take me.”
Sasnovich’s reward for beating Raducanu is a third-round match with former world number one Simona Halep.
The Romanian, seeded 11th, beat Marta Kostyuk 7-6 (2) 6-1.
Seventh-seed Petra Kvitova eased past Arantxa Rus in straight sets while second seed Iga Swiatek was a comfortable winner against Petra Martic.
There were also wins for Anastasia Pavlyuchenkova, former French Open champion Jelena Ostapenko, Victoria Azarenka and Elina Svitolina.
