Coco Gauff lost, then cried, then got a morale boost from her conquerer, the defending U.S. Open champion Naomi Osaka, in a charming gesture at Arthur Ashe Stadium on Saturday night.

After Osaka prevailed 6-3, 6-0 over Gauff in a 65-minute tennis lesson, Osaka made sure the 15-year-old sensation shared the moment with her in the post-match festivities.

After they hugged at the net and Gauff started shedding tears, the two huddled on the sidelines. Osaka convinced Gauff to do the post-match interview in tandem on the court.

“She told me I did amazing and good luck and asked if I could do the on-court interview with her,’’ Gauff said during the on-court interview as tears rolled. “I said no because I knew I’d cry.”

Later on, Gauff gave Osaka, all of 21, kudos for her action.

“I definitely was wanting to leave the court because I’m not the type of person who wants to cry in front of everyone,’’ Gauff said. “I didn’t want to take that moment away from her, as well. She told me it’s better than crying in the shower. She convinced me, like, multiple times to stay. I kept saying no. Finally I said, OK, I’ll do it. I really thank Naomi for that because it was a good moment for me.”

Osaka said she thought of inviting her when she saw some tears at the handshake.

“It was kind of instinctive,’’ Osaka said. ” I wanted to have her head high going off the court — not sad.’’

Gauff held her own for a while in a first set that featured five service breaks but couldn’t sustain the No. 1 seed’s high level, especially when her serve went south (seven double faults).

Coco-mania is over for now but there didn’t seem to be a need for tears after her brave Flushing showing in which she pulled out two three-setters and stood toe-to-toe with Osaka for nearly a set. Then again she hasn’t had her Sweet 16 yet.

“It showed that I’m human,’’ Gauff said. “People usually see my fiery side. A lot of people see the more pumping up side of me, the more fiery side.’’

Father/coach Corey Gauff said the tears were borne of disappointment.

“You’re a competitor, you’re thinking about winning the match,’’ Corey said. “She was mad she didn’t play well. She wanted to win the match.’’

Corey was concerned when her daughter stayed on the court afterward, not realizing Osaka had begged her to stick around. “She recognizes a lot of pressure for Coco to compete at that stage,’’ Corey said.

Ironically, Osaka got misty-eyed too when she addressed Gauff’s family box on-court for doing “an amazing’’ job developing Coco. Their fathers have known each other for years.

Gauff had the crowd but not enough consistency. She wasn’t changing the pace enough against the 21-year-old Japanese-American, who crushed backhands much of the evening, displaying stunning power.

Osaka ran off the last eight games.

But it could be the start of a long rivalry, as the 140th-ranked Gauff keeps rising and looks like a future Grand Slam champion.

“It’s the most focused I’ve been since Australia,’’ said Osaka of her Grand Slam victory in January. “The energy was crazy — even if it wasn’t for me.’’

It was a compelling first set. In her first match on Ashe, Gauff rallied from 3-0 to get the set on serve at 4-3. As Gauff made her comeback, the crowd chanted, “Let’s go Coco, let’s go.’’

“It was hard for me to control the points,’’ Gauff said.

“It’s hard to go on Ashe with that many people,’’ Corey Gauff added. “Wimbledon was good prep but you weren’t playing the No. 1 player. She was nervous. She tried to over-hit.’’

Coco Gauff announced her arrival on the tennis scene at Wimbledon in July when she made the fourth round before losing to eventual champion Simona Halep. Now Gauff may have just lost to the eventual Open champion.

In the first set, when Gauff won her first game by spanking two straight aces, she screamed “C’mon!’’ and the fans exploded and chanted her name. Then she broke Osaka to put the set on serve at 3-2 and Ashe Stadium was in full roar.

“She showed she can play with her,’’ Corey Gauff said. “She showed signs if she gets better sustains and gets more experience it will be a better match for her [next time].’’

Coco Gauff, who won her first two matches here in three sets, has had to limit her match play after the Open because of the tour’s age rules. According to Corey Gauff, Coco may not play on the WTA tour until the 2020 Australian Open.

The tennis world awaits.

“I’m glad I was able to experience that on the biggest stage,’’ Coco said. “Maybe next time I’ll have a different result.”