Defending champion Emma Raducanu of Britain was sent crashing out of the US Open in the first round on Tuesday, losing in straight sets to France's Alize Cornet.

Eleventh seed Raducanu became only the third women's defending champion in history to lose in the first round as Cornet crafted a scintillating performance to seal a deserved 6-3, 6-3 victory on Louis Armstrong Stadium.

The 32-year-old Frenchwoman, ranked 40th in the world, drew on all her experience to outfox the 19-year-old Raducanu, boldly pulling off a string of exquisite drop shots at key moments to set up the victory.

Cornet, who also produced an upset at Wimbledon last month with a straight sets defeat of world number one Iga Swiatek, attributed her recent improvements to maturity.

"I think I'm just handling my emotions better, that's it," Cornet said.

"I guess I'm getting old and getting more mature and now when I have to serve for the match I stay in the match and stay in the present moment and really think about what I have to do.

"I think managing my emotions is just much better and I'm really happy because it shows in my results. It's good because I'm 32. Better late than never."

Raducanu had been the darling of the Flushing Meadows crowd last year, when she made history by emerging from qualifying to claim a fairytale maiden Grand Slam.

That win marked the first time ever a qualifier had lifted a Grand Slam title.

- 'Target on my back' -
But she has since struggled to recapture the form that swept her to an improbable championship crown last year. In three previous Grand Slams this year she had gone no further than the second round.

Her exit on Tuesday sees her join Angelique Kerber in 2017 and Svetlana Kuznetsova in 2005 as the only defending US Open champions who have fallen at the first hurdle.

"Obviously really disappointing, really sad to leave here," Raducanu said afterwards. "It's probably my favorite tournament."

Raducanu, who will nosedive down the rankings after Tuesday's loss, said she hoped to take some time to regroup.

"In a way I'm happy because it's a clean slate. I'm going to drop down the rankings, climb my way back up," she said.

"The target will be off my back slightly. Yeah, I just have another chance to claw my way back up there."

A finely balanced contest was settled by Cornet's ability to show greater composure when it mattered as Raducanu froze.

Cornet had broken Raducanu to lead 4-2 in the first set, only for the Briton to claw her way back in the next game with a break that made it 4-3.

But Raducanu squandered a 40-15 lead on her next service game before double-faulting to gift Cornet a break which left the Frenchwoman 5-3 up and serving for the set. Cornet duly held serve to seize the advantage.

Raducanu, who has been bothered by finger blisters this season, took a medical time out in between the first and second sets to treat the problem once more.

It looked to have paid off as she raced into a 3-1 lead in the second set.

But once again she was unable to make her advantage count, and it was Cornet, with one of several sublime drop shots scattered throughout her victory, who broke back.

Cornet held to love for 3-3 and then broke Raducanu twice more to seal a win which sets up a second round meeting with the Czech Republic's Katerina Siniakova.