Defending champion Naomi Osaka overwhelmed 15-year-old Coco Gauff to reach the US Open last 16 in front of a captivated Arthur Ashe Stadium.

World number one Osaka, 21, won 6-3 6-0 against the home favourite - and later consoled the emotional American in heart-warming scenes.

Gauff matched Osaka for much of the first set, but her game - particularly serve - unravelled in the second.

She produced double faults at crucial times as Osaka broke serve six times.

Osaka, who added the Australian Open title to her maiden major win here last year, will face Swiss 13th seed Belinda Bencic in the fourth round.

Bencic, 22, progressed after her third-round opponent Anett Kontaveit of Estonia withdrew through illness.

'Focused' Osaka too good for Gauff

Even Serena Williams said she could not wait for the battle between Osaka and Gauff after, like many, describing the two players as the future of women's tennis.

Williams, the 23-time Grand Slam champion, admitted the prime-time night match would turn her into a "fan girl" and would not have been disappointed by a competitive start.

Neither was a packed Ashe, which was unusually quiet while an engrossed near-24,000 crowd watched a compelling battle unfold.

Yet the atmosphere soon became flat as Osaka outpowered Gauff - who was aiming to become the youngest player to reach the last 16 since Russian Anna Kournikova in 1996 - to run away with the second set and win in one hour and five minutes.

Gauff, who was playing on the world's biggest court for the first time, began to look a little overwhelmed with the occasion and, shortly after losing the match with a long forehand, fought back the tears.

Osaka tried to console her and also became emotional as she paid tribute to the Florida teenager and thanked her family for raising an "amazing" player.

"I used to see you guys training in the same place as us. The both of us made it and are working as hard as we can," Osaka said.

"I think this is the most focused I've been since Australia, so sorry for playing in this mentality.

"I've watched her play a couple of times and thought she was an incredible mover and had to get going off the bat."

Both players received another vociferous ovation as they walked off court shortly after each other, presumably not for the last time as they look set to contest the sport's biggest titles over the coming years.

Double faults prove costly for Gauff

Gauff has showed remarkable maturity for a player of her age - on and off the court - since becoming a global star with her run to the last 16 at Wimbledon in July.

Powerful strokes and impressive court coverage have been the foundations of her early success, but she largely came undone against Osaka because of her poor serving.

Gauff's service game at Flushing Meadows had been patchy coming into the third-round match, particularly having produced 18 double faults across her opening two victories.

That proved to be her downfall again as she notched another seven and was punished by Osaka.

Handing over a break point in her first service game of the match with a double fault proved an ominous sign, with another changing the momentum of a pivotal eighth game.

Gauff had twice fought back from breaks down in the opener, only for another double fault at 15-0 to allow Osaka to seize control for a 5-3 lead which she converted into a one-set advantage.

The American started the second set with another double fault for 0-30, then threatened to crack her racquet on the court after immediately hitting another first serve into the net.

The teenager suddenly started to look overwhelmed and another double fault handed over the first game, leaving Ashe in virtual silence.

Three more of the same errors came in what proved to be her final two service games as Osaka won the second set in just 29 minutes.

Analysis

BBC tennis correspondent Russell Fuller

Naomi Osaka produced probably her finest performance since the Australian Open.

She hit the ball ferociously hard, and used some mind-bending angles to eventually overwhelm the 15-year-old.

But Coco Gauff's first-set performance was fabulous. Resilient in defence, and full of poise, she twice came from a break of serve down. And all this, at 15, in front of well over 20,000 people in the largest stadium in tennis.

Gauff is currently projected to rise to 105 in the world rankings, but will not be able to play many more tournaments before her 16th birthday.

Age eligibility rules mean she may only be able to play three more events between now and March. The last two months of the WTA season are played in Asia and Europe, so practice and school work may take precedence for the rest of the year.