Bianca Andreescu has stunned six-time US Open champion Serena Williams 6-3, 7-5 to claim her first grand slam title at Flushing Meadows.

Key points: Teenager Andreescu put her fingers in her ears as the New York crowd cheered Williams's short but furious comeback

Teenager Andreescu put her fingers in her ears as the New York crowd cheered Williams's short but furious comeback Down 5-1 in the second set, Williams won 17 of 24 points to draw level at 5-5

Down 5-1 in the second set, Williams won 17 of 24 points to draw level at 5-5 It was the American's fourth grand slam final defeat as she chases Margret Court's record

There were no tears this year — and no controversy — but 12 months on from the extraordinary final between Williams and Naomi Osaka, Williams is still waiting for that record-equalling 24th grand slam title.

It was an uncharacteristically sloppy display from 37-year-old Williams, with Andreescu breaking the American's serve six times in the contest.

Williams threatened a stirring comeback in the second set, winning 17 of 24 points to fight back from 5-1 down to draw level at 5-5.

But 19-year-old Andreescu held her nerve in the face of Williams's furious onslaught amidst a cacophony of noise from the parochial Arthur Ashe Stadium crowd to become Canada's first ever grand slam champion.

"It's so hard to explain. I'm beyond grateful and truly blessed," Andreescu said.

Andreescu became the first Canadian to win a major title. ( AP: Charles Krupa )

"This year has been a dream come true and to be able to play on this stage against a true legend of the sport is amazing."

That legend, whose quest to match Margaret Court's record of 24 grand slam titles will now head to Melbourne in the new year, was typically gracious and complimentary of her young opponent.

"Bianca played a special match," Williams said.

"It was incredible tennis out there … I wish I could have played a little better.

"If anyone could win — outside of Venus — I'm happy it's Bianca."

It was Williams's fourth grand slam final defeat since she drew within one title of Margaret Court's record of 24 singles championships.

Williams's last grand slam victory came at the 2017 Australian Open before she suffered complications after giving birth to daughter Alexis.

Frenetic start sets the tone

Serena Williams was given the run-around by her teenage opponent. ( AP: Charles Krupa )

It was clear from the start that the court would be no place for the faint-hearted, as both women started with a ferocious intensity.

Not many players on the tour can go toe-to-toe with Williams's power from the baseline.

But you can now add Andreescu's name to the short list of players who can.

However, Williams's errant first serves contributed to her own downfall, the veteran hitting just 45 per cent of her usually reliable first serves as well as hitting eight double faults over the course of the match.

Andreescu opted to let the six-time US Open champion serve first, hoping to play on any residual nerves that Williams may have had. It worked.

Never looking out of place on the grand slam stage, Andreescu broke Williams in that first game thanks to two double faults and did not look back, taking a nerveless first set 6-3 in just over 40 minutes.

Andreescu was meeting fire with fire, matching Williams's power with unerring accuracy in the big moments.

The first break point Andreescu faced came in the eighth game, and she responded with a 166kph, Serena-like ace out wide.

Bianca Andreescu broke Williams in the first and last game of the match. ( AP: Charles Krupa )

Williams was playing a reflection of herself, a player not afraid to trade blows from behind the baseline, aided by prodigious topspin that made returning fire all but impossible.

Andreescu was dictating the match, forcing the usually dominant Williams onto the defensive in almost every point.

The champion was rattled, Andreescu taking advantage of Williams's first serve woes to monster her still-powerful second serve with probing forehands that peppered the baseline.

It was a third double fault of the set that handed Andreescu the first set, leaving the pre-eminent player of her era visibly chastising herself in her chair, seemingly talking herself out of the contest.

Andreescu withstands late Serena surge

An upset was on the cards, the celebrity-strewn crowd at Arthur Ashe Stadium looking increasingly nervous.

Breaking Williams's first service game of the second set to love thanks to yet another double fault sent the upset-klaxon into overdrive and when the Canadian raced into a 5-1 lead in the second set, headlines were starting to be written.

But you can never underestimate Williams's tenacity and ability to pounce when her back is against the wall.

The roof at Arthur Ashe Stadium was open, the rain of Friday replaced by picturesque high cloud. If it hadn't, the noise that emanated from the raucous crowd during her phenomenal fightback would have blown it clean off.

"I was just fighting at that point, just trying to stay out there a little bit longer," Williams said.

"Honestly the fans were cheering so loud that it inspired me a little bit."

Inspiring Williams, but intimidating Andreescu.

Serena Williams was broken six times in the match as her first serve malfunctioned. ( AP: Charles Krupa )

"Definitely the crowd [was a challenge]," Andreescu admitted.

"I know you guys wanted Serena to win, so I'm so sorry.

"Obviously I was expecting Serena to fight back. But I just tried to block everything out."

Andreescu was reduced to the time-tested method of putting her fingers in her ears as the bleachers erupted into a cacophony of noise in response to Williams's charge — and it clearly worked as the teenager showed a maturity beyond her years to regain the ascendancy and broke Williams a final time to claim the match.

This time last year, Andreescu failed to make it out of qualifying for the US Open.

Now, she's only looking forward.

"It hasn't been easy [over the last two years], so I just have to say thank you and let's keep going."