Under a hot sun not far from Hillside Avenue in Jamaica, Queens, Naomi Osaka couldn’t get the smile off her face Thursday.

Osaka was feeding balls to dozens of kids in a tennis clinic at Detective Keith L. Williams Park, courts on which she grew up playing.

The kids ranged from 5 to 16. Every well-hit volley and resounding forehand that sailed out of Osaka’s reach brought sheer joy for her. Osaka posed for pictures and spoke to the more than 150 people who gathered in the park.

Teaming with her sponsors at BodyArmor, a sugar-free energy health drink, Osaka spent the past several months redesigning the courts and funding their refurbishment.

Five of the park’s dilapidated cracked courts now glisten in royal blue amid Osaka’s decorative artwork. Thursday was the big unveiling — murals of Osaka’s past surrounding the tennis lines as a highlight.

No, this hasn’t been an easy summer for Osaka, starting with her French Open withdrawal after she announced she would not do post-match press conferences due to the pressures.

She withdrew from Wimbledon, too, amid an international debate on whether Osaka’s revelation of mental health issues warranted boycotting press conferences.

The 23-year-old is the third seed and defending champion entering the U.S. Open on Monday, eight miles away at Flushing Meadows, but she doesn’t come in with much momentum.

Hence, these are the off-the-court moments Osaka cherishes, when the fame is all worth it, seeing the bright faces of the kids swinging their rackets.

Osaka was born in Osaka, Japan, moving to this section of Queens at age 3. Chris Mitchell, one of the locals and a clinic volunteer, remembers Osaka on these courts long ago hitting alone with her father.

Osaka finally moved out of the congested neighborhood when she was 8 — off to the tennis hotbed of South Florida.

“It feels special to be able to give back to the community in such a meaningful way,’’ Osaka told The Post via email. “I want these courts to be a place that kids not only want to come and play on, but I also wanted to leave a message behind that inspires the community. My sister Mari and I worked on a mural that ties in some of our personal background, as well as places that inspire and motivate me to keep playing the game.

“I just hope that everyone remembers that tennis is a game and is meant to be fun.”

Her court murals depict logos of distances to Japan, Los Angeles and Haiti, where her father is from. There are big purple letters spelling “Queens” and paintings of various colored tennis balls.

“I loved living on the East Coast and I remember mostly spending time with my dad and sister on the courts,’’ Osaka said. “We practiced a lot and I remember spending many hours learning skills with my dad, then playing with the local adults. I also remember the park being really busy and enjoying the people watching as there was always a lot happening there.’’

Osaka has won two U.S. Open titles — including last year’s fan-free event. She’ll be the hometown hero starting Monday.

“What I really enjoy most about playing at the Open is that nostalgic feeling of coming back to Queens, where it all started,’’ Osaka said. “When I started talking about doing something that gave back to community it felt like it was meant to be.’’

Osaka noted BodyArmor, a non-artificial premium health sports drink, is headquartered in Queens. Its founder is Queens native Mike Repole.

Joining Osaka for the court’s unveiling was another New York-based sports celebrity — Jazz All-Star Donovan Mitchell, who grew up in Westchester County and Greenwich, Conn., and also is a BodyArmor spokesman.

Mitchell, who spends his offseasons in Greenwich, will attend the Open for the first time this week to watch Osaka.

“I don’t know too much about tennis but I do know what she’s been through and what she’s done at a young age,’’ Mitchell told The Post. “She’s a tremendous athlete. I’m a fan. I love and respect what she does on the court and off the court. She’s inspiring. I told her I have nine others on the floor with me. The stage is her and her opponent. That brings a whole ’nother level of nerves I can’t imagine. She’s phenomenal.’’

Last year, Osaka’s profile rose to new heights when she donned a different mask naming victims of police brutality during her path to the Open final.

“Last year was a really special year at the Open,’ Osaka said. “I felt like it wasn’t just about what happened on the court, but helping to connect and inspire off the court also gave me a really feeling of community and connection.’’

Osaka didn’t want to comment about critics who feel conducting press-conferences is part of the job as a professional athlete. Osaka is on the docket for Friday’s U.S. Open Media Day.

“Like any tournament I am coming in without putting any added pressure on myself,’’ Osaka said. “I am going to do the best I can in preparation and when I hit the courts.’’