It was a performance that left the New York crowd stunned, with some spectators in the stadium almost laughing at the implausibility of what they had just witnessed.
There have been many surprises over the years on the courts at Flushing Meadows, but nothing quite like this.
The idea that a teenager ranked 150 in the world - a qualifier who has barely played on the WTA Tour - could win the trophy here seemed preposterous.
That Emma Raducanu could do it without dropping a set is one of the most astounding achievements in the history of women's tennis.
Champion Raducanu thanks the New York crowd for their support
She held the trophy aloft after firing an ace to win the championship, quite literally leaving blood on the court.
Raducanu has won admirers in the Arthur Ashe stadium and all over the world.We spoke to spectators as they emerged from the match and it was striking that on a date that haunts New York - Saturday was the 20th anniversary of the September 11 attacks - there was a sense of inspiration at having watched a young woman born after 9/11 defying the sporting odds.
Some Britons in the crowd told me it was the greatest sporting triumph they had seen in their lifetimes.
Match spectators react to Raducanu's stunning US Open win
After the match and the trophy ceremony, Raducanu spoke to journalists and said she had been living inside a bubble.
Her team had kept the pressures of the British media from her. She said she had little idea what the reaction back home was, and she hadn't even made any firm plans to return to London.
ITV News's Robert Moore takes a look at the next steps for the teen champion
But one man who has to think of the future is Iain Bates, who leads the LTA, and could barely believe what he was seeing on Arthur Ashe last night.
When I met him a few minutes after the match, he was still shaking his head, wondering how to leverage this moment for grassroots tennis in Britain.
What we have witnessed here is a privilege: the emergence of a genuine British sporting phenomenon.
The challenge is going to be to relish Raducanu's success while protecting her from wild expectations and media intrusion.
Iain Bates, who leads the LTA, could barely believe what he was seeing on Arthur Ashe on Saturday night
Women's tennis is littered with young stars who ended their careers prematurely amid excessive scrutiny and pressure, from Jennifer Capriati to Tracy Austin.
Even in this current generation, the struggles of Naomi Osaka are a reminder that even the greatest tennis players - male and female - are also vulnerable to the roller-coaster ride of the tour.
Let us hope that with our new superstar from Bromley we all understand that she's a young woman of prodigious talent who is at the very start of a career that will see setbacks as well as triumphs.