Ms Osaka is the first Japanese player to win a grand slam title; Ms Osaka beat Ms Williams 6-2 6-4
Japan is celebrating its first ever Grand Slam tennis win after Naomi Osaka's US Open win over Serena Williams 6-2 6-4 at Flushing Meadows.
Osaka stayed calm as Ms Williams went into meltdown after the umpire imposed a series of penalties.
She was later in tears waiting to be given her trophy as the partisan crowd booed the match officials.
The 20-year-old was born in Japan to a Japanese mother and a Haitian father but was raised in the US.
Prime Minister Shinzo Abe congratulated Ms Osaka on Twitter, thanking her for "giving Japan a boost of inspiration at this time of hardship" - an apparent reference to last week's deadly Typhoon Jedi and the Hokkaido earthquake that killed dozens of people.
Tennis is less popular than other sports such as baseball, football and sumo wrestling in Japan, but after her win the Yomiuri newspaper said Ms Osaka was a "new heroine Japan can be proud of".
"The combination of her strength and childlike innocence is her charm," the newspaper said.
Osaka faced hostility during what should have been a moment of joy as boos and whistles rang out around the Arthur Ashe stadium, and lowered the visor she had been wearing to hide her tears.
Williams then put her arm around her and said: "Let's make this the best moment we can, let's give everyone the credit where credit's due and let's not boo any more."
"I know everyone was cheering for her and I'm sorry it had to end like this," said Ms Osaka. "I just want to say thank you for watching the match."
She said it was "always my dream to play Serena in the US Open finals," and, addressing her opponent, she said: "I'm really grateful I was able to play with you."
She then bowed, to applause from the crowd.
Ms Osaka - who also holds US citizenship - is the latest dual heritage athlete to rise to prominence in Japan, which has traditionally viewed itself as an ethnically homogenous society.
She along with sprinter Asuka Cambridge, baseball player Yu Darvish and judo star Mashu Baker are helping change public attitudes.
"Japanese are getting more accustomed to people from other cultures," Hirotaka Matsuoka, a professor of sports marketing at Waseda University in Tokyo, told Reuters.
"If an athlete isn't half-hearted and really makes it clear they are representing Japan, then the public will support them."
About one in 50 Japanese newborns is mixed race but the "hafu" - the Japanese term for a bi-racial person - still face prejudice.
-- Courtesy of BBC Sport