British teenager Emma Raducanu completed the greatest underdog title run in tennis history on Saturday, becoming the first qualifier to capture a Grand Slam crown by defeating Canada's Leylah Fernandez in the US Open women's final.

The 18-year-old was the first British woman in 44 years to win a Slam crown after beating 19-year-old left-hander Fernandez 6-4, 6-3 to take the $2.5 million (2.1 million euro) top prize.

"I knew I would have to dig deep," Raducanu said. "It was an incredibly difficult match but I thought the level was really high. I had to play some of my best tennis."

It was a stunning achievement for the unheralded 150th-ranked teen, who didn't drop a set in three qualifying matches and seven main-draw matches over two weeks in producing a stunner for the ages.

Raducanu is the youngest Slam champion since Maria Sharapova at 17 in 2004 at Wimbledon.

Not since Virginia Wade in 1977 at Wimbledon had a British woman taken a Slam singles title, with Raducanu the first Briton to claim the US Open crown since Wade in 1968.

Queen Elizabeth II was among the first to pay tribute to Raducanu's incredible triumph.

"It is a remarkable achievement at such a young age, and is testament to your hard work and dedication," the British monarch said in a statement.

Wade and British men's tennis legend Tim Henman were among a sellout crowd of 23,700 that created an electric atmosphere at Arthur Ashe Stadium in the first-ever women's Slam final between unseeded players.

"It means so much to have Virginia here and also Tim and to have such British legends and icons, to follow in their footsteps and it gave me the belief I could actually do it."

Raducanu has had the fewest Slam starts of any women's Slam winner, reaching the fourth round in July at Wimbledon in her only prior Slam appearance.

Fernandez, ranked 73rd, had ousted defending champion Naomi Osaka, second-ranked Aryna Sabalenka and fifth seed Elina Svitolina in her epic run to the final.

"I'm very proud of myself the way I played the last two weeks," Fernandez said. "I hope to be back here in the finals and having the right trophy," added a tearful Fernandez, who paid tribute to New York as the city marked the 20th anniversary of the 9/11 attacks.

"I know it's especially hard on this day for New York," she said. "I just want to say I hope I can be as strong and resilient as New York has been the past 20 years."

Raducanu is the youngest US Open champion since 17-year-old Serena Williams in 1999 and the first US Open women's champion not to drop a set since Williams in 2014.

The prodigy showdown was the first all-teen Slam final since Williams beat 18-year-old Martina Hingis for the 1999 US Open title.

"Both of us were playing fearless tennis for two weeks," Raducanu said. "I hope we play each other in many more tournaments and hopefully finals."

- Blood, sweat and tears -

After an early exchange of hard-fought breaks, Raducanu broke in the 10th game to take the first set, blasting a forehand winner after 58 minutes.

In the second set, Fernandez broke to 2-1 but Raducanu blasted a backhand cross-court service return winner to equalize 2-2 and later whipped a forehand passing winner by the Canadian to break for 4-2.

Fernandez saved two match points in the eighth game and held to 5-3, then earned a break chance at 30-40 in the ninth.

But on the point, Raducanu skidded on her left knee and opened a bleeding cut. The match was halted while a trainer bandaged the wound as Fernandez spoke with the referee.

"I didn't know how serious her fall was, so that's why I went to see the official," Fernandez said. "It was just too bad it happened in that specific moment with me, with the momentum. But it's sports, it's tennis. Just got to move on."

When play resumed, Fernandez sent a forehand long to squander the break chance and Raducanu won after an hour and 51 minutes on her third ace, leaving Fernandez in tears.

"I was going for that serve the whole match. I can't believe I finally hit it," Raducanu said. "I was just praying not to double fault."

‘Living the dream, reality can wait’

Emma Raducanu fell asleep as a little girl to visions of running through the stands to celebrate a Grand Slam title and lived the moment Saturday after capturing the US Open title.

The British 18-year-old beat 19-year-old Canadian Leylah Fernandez 6-4, 6-3 to become the first qualifier to win a Slam title, rolling through 20 sets without loss to hoist the trophy.

"It's an absolute dream. You just have visions of yourself going up to the box, hugging everyone, celebrating," she said. "For that moment to actually happen, I'm just so grateful."

Her childhood visions returned as her epic run pushed her to becoming the youngest Grand Slam champion in 17 years and the youngest US Open winner since 17-year-old Serena Williams in 1999.

"Going to celebrate with your team, trying to find your way up to the box, just seeing them after the match, that has been playing in my head a couple nights. I've fallen asleep to that," she said.

"To have the belief I did and actually executing, winning a Grand Slam, I can't believe it."

Raducanu has adopted a nothing-to-lose attitude and Slam success ensures it won't change any time soon.

"I don't feel absolutely any pressure," Raducanu said. "I'm still only 18 years old. I'm just having a free swing as anything that comes my way. That's how I faced every match here in the States.

"It got me this trophy so I don't think I should change anything."

Raducanu never dropped more than five games in any set and that happened only one, in qualifying, although she insisted every win had its challenges.

"I faced a lot of adversity in every single one of my matches," she said. "What I did very well this tournament was press in the moments that I really needed to."

While she may have faced adversity, she has not faced reality, setting aside her cell phone and the world outside to focus upon the US Open.

"I still haven't checked my phone. I have absolutely no idea what's going on outside of the little world that we're in here," Raducanu said.

"The biggest triumph for me is how I managed to just not think of absolutely anything else except for my game plan, what I'm going to execute. I just completely zoned in and focused on my craft.

"I think that's definitely the biggest thing that's probably helped me to win this title."

So when it comes to things like how her US Open title will change her life, she hasn't given it a thought. She can't even say what's up next week.

"I haven't thought of any of that," Raducanu said. "I have no idea when I'm going home. I have no idea what I'm doing tomorrow. I'm just really trying to embrace the moment, take it all in.

"I definitely think it's the time to just switch off from any future thoughts or any plans, any schedule. I've got absolutely no clue. Right now, no care in the world, I'm just loving life."