Naomi Osaka Gifts Olympic Pin To Young Fan At U.S. Open, Thanks For Cheering!

Naomi Osaka just made one young fan's day at the U.S. Open on Monday ... by gifting her a collectible Olympics pin as a "thank you" for showing so much support during her first-round match!!

The 23-year-old superstar advanced to the second round after winning in straight sets just hours ago ... and the little girl was cheering for her the entire time!!

Osaka -- who had an early exit from the 2020 Olympic Games -- said she had a few trading pins left over from her time in Tokyo ... so she decided to give an extra to her biggest fan in the stands!!

FYI -- Olympic pin trading is a tradition that goes back more than a hundred years ... with athletes, reporters and fans all swapping the little items during the Summer and Winter Games.

Osaka was asked about the gesture in her post-match interview ... saying, "I just heard her when I was playing my match and she was so cute."

"So, thank you for cheering me on!"

The camera then showed the fan smiling from ear-to-ear -- at least, we're assuming, 'cause the whole mask situation -- and waving back at Osaka.

"I thought it would be a nice little memory," the #3-ranked player added.