Naomi Osaka knows how to put a smile on her fans.

The defending US Open champion gifted an Olympic pin to a young fan after registering a straight sets win over Czech Republic's Marie Bouzkova on Monday. And the video of the gesture is going viral on the Internet.

"I just heard her (young fan) when I was playing my match and she was so cute. So, um... thank you for cheering me on and on. But yeah, in the Olympics, we got little pins that we were supposed to pass around to other players like trading pins. And I wasn't there (at the Olympics) for a long time so I have a couple in my bag left over. I thought it would be like a nice little memory," Osaka said.

Here's the video:

Naomi is on track to become the first back-to-back US Open women's champ since Serena Williams, who bowed out of the Grand Slam with a torn hamstring. Williams won her third US Open title in 2014.

Last year the Grand Slam was conducted behind closed doors due to coronavirus pandemic. But this year, spectators have been allowed, and Naomi says the "energy is unmatched".