NEW YORK, United States (AFP) — British teenager Emma Raducanu completed the greatest underdog title triumph in tennis history yesterday, becoming the first qualifier to capture a Grand Slam title with a straight sets defeat of Canada’s Leylah Fernandez in the US Open women’s final.

Raducanu, 18, was the first British woman in 44 years to win a Slam crown after beating 73rd-ranked 19-year-old left-hander Fernandez 6-4, 6-3 to take the US$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 on the New York hardcourts while producing a stunner for the ages.

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 remarkable win.

“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 sell-out crowd of 23,700 that created an electric atmosphere at Arthur Ashe Stadium in the first-ever women’s Slam final between unseeded players.

Fernandez, who turned 19 on Monday, had ousted defending champion Naomi Osaka, second-ranked Aryna Sabalenka, fifth seed Elina Svitolina and three-time Slam winner Angelique Kerber in her epic run to the final.

Raducanu is the youngest US Open champion since Williams in 1999 and the first US Open women’s champion not to drop a set since Williams in 2014.

The showdown of prodigy talents was the first all-teen Slam final since 17-year-old Serena Williams beat 18-year-old Martina Hingis for the 1999 US Open crown.

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 saved five break points in her opening service game of the match before finally surrendering the 10-minute game on a netted forehand to give Raducanu a 2-0 edge.

Fernandez broke back in the third game, Raducanu netting a backhand on the fourth break point she faced.

But Raducanu broke in the 10th game to take the set, blasting a forehand winner to seize the lead after 58 minutes.

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

Raducanu had two match points on Fernandez’s serve in the eighth game but sent a backhand wide and netted a forehand as Fernandez held to 5-3.

Fernandez grabbed a break chance at 30-40 in the ninth game when Raducanu skidded on the court on her left knee and opened a bleeding cut. The match halted while a trainer bandaged the wound.

When play resumed, Fernandez sent a forehand long to squander the break chance and Raducanu ended matters after an hour and 51 minutes on her third ace of the match.