Naomi Osaka talks with Coco Gauff after their match in the third round on day six of the 2019 US Open tennis tournament. Reuters

Defending champion Naomi Osaka consoled a tearful Coco Gauff after a crushing US Open victory on Saturday in a showdown billed as "the future of women's tennis" while Rafael Nadal cruised into the last 16.

World number one Osaka overpowered 15-year-old Gauff 6-3, 6-0 in 65 minutes to keep her title defense on track before sharing a warm embrace with an opponent overwhelmed by the occasion in the New York spotlight.

The emotional clash was followed by tearful on-court interviews, Osaka asking Gauff to join her with the microphone as they met at the net.

Naomi Osaka consoles Coco Gauff after their third round match. Reuters

"It was kind of instinctive because when I shook her hand, I saw that she was kind of tearing up a little. Then it reminded me how young she was," Osaka said.

"I wanted her to have her head high, not walk off the court sad. I want her to, like, be aware that she's accomplished so much and she's still so young."

Osaka said the match was one of her best since winning the Australian Open title.

"This is the most focused I've been since Australia," Osaka said, telling Gauff: "Sorry for playing you in this mentality."

Naomi Osaka listens as ESPN’s Mary Joe Fernandez interviews Coco Gauff. Reuters

The primetime third-round clash at Arthur Ashe Stadium pitted 21-year-old Japanese star Osaka against the American, who made a fourth-round Wimbledon run on her Grand Slam debut.

Serena Williams, the 23-time Grand Slam champion, called it "the future of women's tennis", while Novak Djokovic labeled Gauff "a new superstar".

But Gauff, the youngest player through to the third round here since Anna Kournikova in 1996, struggled in her first match under the lights on Ashe.

"She (Osaka) did amazing and I am going to learn a lot from this match," Gauff said. "She's the number one player in the world right now, so I know what I need to do to get to that level."

Osaka next faces Swiss 13th seed Belinda Bencic, who was handed a walkover when Anett Kontaveit withdrew due to illness.

Agence France-Presse