Naomi Osaka runs for a short ball during her match against Coco Gauff at the US Open on Saturday. Photo: VCG

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

World No.1 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.

"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."

The prime-time 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 US Open third round 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 No.1 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.

Three-time champion Nadal returned from an extended rest to dispose of 170th-ranked South Korean qualifier Chung Hyeon 6-3, 6-4, 6-2, having benefited from three days off after a walkover.

The Spanish second seed will meet 2014 champion Marin Cilic for a place in the quarterfinals.

"I'm happy to be in the fourth round for one more time. It was a good match," said Nadal, who quit with injury against Juan ­Martin del Potro during last year's semifinal.

Cilic, the 22nd seed and 2017 Wimbledon finalist, took out top US hope John Isner in four tight sets.

Sixth seed Alexander Zverev made it to the second week in New York for the first time after fighting past Aljaz Bedene 6-7 (4/7), 7-6 (7/4), 6-3, 7-6 (7/3).