Naomi Osaka, the defending U.S. Open champion, doesn’t expect to suffer a letdown when she faces 13th seed Belinda Bencic in a fourth-round bout at noon to kick off the Labor Day card at Arthur Ashe Stadium.

Osaka even unintentionally delivered a noteworthy boast after her 6-3, 6-0 romp over 15-year-old phenom Coco Gauff late Saturday.

Osaka won last year’s Open, then the next Grand Slam event, the Australian Open last January. Since then, the Japanese American has been mediocre, admitting recently that tennis isn’t as much fun as in 2018.

However, Osaka seems supercharged during this Open — brilliant and focused against Gauff, belting 26 winners and wielding a fierce service return.

“The thing with me is I get better as the tournament goes on,’’ Osaka said Saturday night. “Like, it’s not even a skill sort of thing, it’s just I trust myself more. The last two [Grand Slams] I was in the round of 16, I won it, if that answers …’’

Osaka interrupted herself at that juncture.

“I don’t want to say that,’’ Osaka said. “That’s bold. Don’t say that.’’

The quirky 21-year-old laughed and added a dose of modesty: “Listen, I’m just out here trying my best. I’m just going with the flow at this rate. I’ve never defended a Grand Slam [title] before.’’

It was difficult not to imagine a women’s tennis future dominated by Osaka and Gauff, who could be just two years away from being a Grand Slam contender.

The scene at the match’s end was compelling theater. Osaka staged a powwow with Gauff on the sidelines after the handshake when she noticed Gauff crying. Osaka convinced Gauff to stick around to do the on-court interview together.

Osaka wears her emotions on her sleeve, as evidenced by last year’s Open championship ceremony when she started crying while the fans booed and sided with Serena Williams.

Osaka also started crying on the court Saturday night when she saluted Gauff’s parents. Osaka can’t escape teary moments in Flushing.

“I think she proved she’s a true athlete,’’ Gauff said. “The definition of an athlete is someone who, on the court, treats you like they’re your worst enemy, but off the court can be your best friend. I think that’s what she did [Saturday].’’

Osaka admitted she’s not yet close to Gauff, but gave thoughtful reasons for begging her to stay on the court, not wanting her to leave the court alone and “sad.”

The worry, Osaka said, is the premature expectations for a 15-year-old, who only one year ago lost in the quarterfinals of the junior Open.

“Honestly, like, I know that you guys [the media] are kind of coming at her with love, too,’’ Osaka said. “But I feel like the amount of media on her right now is kind of insane for her age. I just want her to, like, take care of herself.”

In January, Osaka staged a stunning split with her coach Sascha Bajin even after winning her second slam event, in Melbourne. She hasn’t been the same since, losing in the third round at the French Open and first round at Wimbledon.

She entered the Open as the No. 1 seed, though she suffered a left knee injury in last month’s tune-up in Cincinnati. She is wearing a wrap on her leg.

In the 22-year-old Bencic, Osaka faces a Swiss foe who has gotten the better of her. Bencic holds a 3-2 head-to-head record, having won their past three meetings — a tour event in Madrid, the prestigious Indian Wells in 2019 and last year at the Hopman Cup.

Osaka said the match will be “super challenging.’’

“I just expect a fight,’’ Osaka said. “She doesn’t really ever give up. She kind of fights for every point. I know that’s going to be a really difficult match for me.”

It probably won’t be as emotionally charged as Saturday night, and Osaka, who was born in Japan but lived on Long Island from ages 3 to 9, will have the fans on her side this time.