But like much of Japan, they are more muted in backing — or understanding — her campaign against racial injustice in the United States. Unlike the U.S., Japan has relatively few immigrants and has a generally lower level of awareness about racism — even at home.
Osaka was born in Japan to a Japanese mother and a Haitian father, but moved to the United States when she was three and was raised there.
Before each of her seven U.S. Open matches, she wore a mask with the names of Black Americans who died as the victims of violence.
Osaka is expected to compete for Japan in next year's Olympics and, like many athletes, may want to use that stage to deliver her message; in Osaka's case, the Black Lives Matter campaign.
The International Olympic Committee prohibits displays of “political, religious or racial propaganda” on the Olympic medal podium under its so-called Rule 50. But many athletes are pushing for more rights to speak out at upcoming Olympics.
Some people lobbying for change have said “anti-racist” speech is not political speech.
The Associated Press contacted several of Osaka's sponsors. Forbes magazine listed her last year as the world's richest female athlete with earnings of $37.4 million in the previous 12 months.
The reaction of Japanese watch-maker Citizen Watch Co. was typical of the responses. The company declined to comment on the masks, but expressed delight in an official statement that the tennis star was wearing one of its products — a Naomi Osaka watch with a yellow band during the U.S. Open.
Sports equipment manufacturer Yonex Co. expressed support for Osaka’s feelings, while also stressing that she won her third Grand Slam using one of its rackets.
"National borders and racial discrimination should not exist in sports, and we are carrying out our business activities with hopes that everyone who takes part in sports around the world will have fun. We think Ms. Osaka’s actions reflect our basic stance, and we respect her actions.”
Nissin Foods — the instant noodle maker — said Osaka's third Grand Slam win underlined the spirit behind the company’s “Hungry to win” slogan, and looked forward to her participation in the Olympics.
But when asked about the masks and Osaka's campaign against racial injustice, the spokesman declined comment calling it “her personal matter.”
Automaker Nissan Motor Co. said it planned no statement.
Some response on Japanese social media has been negative, lashing out at Osaka. Of course, there has also been ample praise.
Negative outbursts against people who stand out can be common in Japan, where conformity and teamwork are valued, and individualism is often seen as selfish and unbecoming.
The statement from the Japanese Prime Minister’s Office made no reference to Osaka's masks or any mention about racial injustice, saying on Twitter: “Congratulations. It was a full-set comeback from behind, and you never gave up till the end. Thanks for inspiring us.”