At the start of 2021, few outside British tennis circles had heard of Emma Raducanu. At the end of the year, the 19-year-old is a national superstar and known around the globe.

Three months on, the triumph that transformed the Bromley teenager from a 499-1 pre-tournament outsider to the BBC Sports Personality of the Year has been revisited in a BBC Radio 5 Live documentary.

Featuring interviews with British tennis legends Virginia Wade and Tim Henman, plus members of Raducanu's backroom team, 'Emma Raducanu: Fairytale of New York' will be aired at 20:00 GMT on Thursday.

This is a taste of the documentary's insight into one of the greatest achievements and most incredible stories in the history of sport.

Arriving in New York: 'Her body was toast'

A couple of months before the US Open, Raducanu was launched into the conscious of the British public with a scintillating run at Wimbledon.

Having been given a wildcard to her home Grand Slam, she reached the last 16 before breathing problems forced her to retire against Ajla Tomljanovic in what was then the biggest match of her career.

Wimbledon was her second professional tournament and to reach the US Open main draw in only her fourth, she would have to win three qualifying matches in New York.

Henman, the former British men's number one, is close friends with Andrew Richardson, the coach who helped guide Raducanu to the US Open title.

"If you had said to Emma and Andrew before qualifying 'would you sign a document to guarantee winning three qualifying matches but lose in the first round of the main draw?' I think there is a fair chance both would have signed on the dotted line," said Henman.

That view is supported by Will Herbert, the physio who Raducanu called 'The Mechanic' for keeping her fit during the US Open.

"My memory of seeing Emma for the first time in New York is that her body was toast. She was exhausted," Herbert recalled.

"She had some pretty successful weeks in Chicago so her body was a bit of a mess. Our initial aim was to get her through 'quallies'. That's where we felt she was.

"The mobility in her back had gone and muscles were fatigued. Our aim was to try and restore normal movement."

Despite those concerns, there were signs from the day she touched down in New York that Raducanu meant business.

Iain Bates, the LTA's head of women's tennis, remembers her being "kicked off" her practice court after her allotted hour had expired and Raducanu being determined to find another court so she could practise "five or 10 minutes more of finishing forehands".

"Even at the start of that week, she was right on it," said Bates.

So it proved as, in heat that topped 35C at Flushing Meadows, she backed up her Wimbledon exploits with three assured wins to earn her place in a first overseas Grand Slam main draw.

The opening rounds: 'It was clear the level was very high'

Like most fairytales, Raducanu's story includes a twist of fate that altered the course of her journey.

American 13th seed Jennifer Brady - who reached the Australian Open final earlier in the year - was supposed to be the Briton's first-round opponent.

But she withdrew because of a knee injury, so Raducanu faced 128th-ranked Stefanie Vogele instead.

Raducanu was a break down in each set against the experienced Swiss, but won 6-2 6-3 with her seventh match point after a slight wobble.

Next up was China's Shuai Zhang, a 32-year-old ranked 101 places higher and with more than 500 career match wins.

Raducanu delivered another impressive display that belied her youth and inexperience, sweeping Zhang aside with a confident and aggressive performance.

Henman had watched Raducanu's qualifying matches back home before flying out to cover the main draw in his role as a television commentator.

"One element that struck me immediately was the level of her play," said the six-time Grand Slam semi-finalist.

"The conditions were quite quick, the ball was lively, but the way she was hitting and moving, dictating play, was very impressive from someone ranked 150th in the world."

The scoreline alone did not fully illustrate her superiority - but it did in her next match against Spain's Sara Sorribes Tormo.

Tormo had recently beaten world number one Ashleigh Barty at the Olympics but had no answer to Raducanu's power and precision in a 6-0 6-1 thrashing.

"It was one of the big moments of the tournament for Emma," said Henman.

"It was that detail and focus of attention to the strategy of Emma playing how she wanted, hitting spots on serve and being really aggressive from the back of the court.

"That's when you knew the level of play was incredibly high. At that stage, for me, the question was: 'Can she sustain it?'"

The second week: 'Now you felt she could win it'

The buzz around Raducanu had started to build.

She had been a popular attraction in the first week, and fans now packed around the smaller outdoor courts to catch a glimpse of her playing, then waited around for selfies and autographs.

With a beaming smile, Raducanu fulfilled every request and her enjoyment on and off court was clear to see.

There was, however, a steely determination for the experience to continue.

The next obstacle was facing the last remaining American woman in the draw in Arthur Ashe Stadium - and Raducanu recovered from a slow start to see off Shelby Rogers.

Herbert said: "After every match Andrew would turn to me and say: 'What's happening Will? What's going on?' I would reply: 'I have no idea.'"

In the quarter-finals Raducanu met Swiss 11th seed Belinda Bencic, who was fresh from winning the Olympic title and a considerable step up in pedigree from her previous opponents.

"The first time I thought Emma could win the title was after she beat Bencic," said Bates.

Raducanu again oozed composed execution and clarity of thought in another straight-set win.

The following day, she did the same against Greek 17th seed Maria Sakkari.

Not only did Raducanu have no day off between the matches, she also dealt with the new experience in playing under the lights on Ashe.

"Emma was managing to impose herself and force her opponents to make mistakes. Those wins were really special. It was an absolute joy to watch," said Wade.

The final: 'Looking back, it was so surreal'

Almost three weeks after she had arrived in New York, Raducanu was preparing to play in the final against another teenager, Canada's Leylah Fernandez.

Herbert says there was little sign of nerves from the Briton in the build-up.

"You never know how people react to a first Grand Slam final. Some people crumble and some people embrace it. She was taking it in her stride."

The pre-match knock-up on Ashe was less assured, according to Henman.

"It was one of the worst warm-ups I've seen in a long time," he laughed. "But when the umpire called time and they started going, the level of both players from point one was exceptional."

As she had all tournament, Raducanu trusted her game in the showdown. Even when two championship points were missed, she maintained her belief and composure to seal a stunning triumph nobody had predicted.

"The level she was able to build day after day just took everybody's breath away," said Bates.

"But the poise she played with, the class she showed, and the enormity of the achievement, we all take a step back now and look back with enormous pride."

Wade was among the first to greet Raducanu as she came off court.

"We found our way down to the players' lounge - I had to be the first in line to hug her," said the 76-year-old.

"It was one big buzz. Everyone was so excited. It was the hug line."

Herbert, Richardson and Henman celebrated with beers, champagne and a platter of cheese.

Once the new champion had completed her media duties and been fitted for her victory dress, the entourage left Flushing Meadows at 11:30pm. The celebrations continued until about 5am in their hotel, accompanied by plenty of sushi and more champagne.

"Every now and then I think about it and just have a little chuckle. It was so surreal," reflected Herbert.

"It unfolded just beautifully. That's the only way I can describe it."