Calm and collected: Naomi Osaka hoists the trophy after her historic win at the US Open. Picture: JULIAN FINNEY/GETTY IMAGES
Calm and collected: Naomi Osaka hoists the trophy after her historic win at the US Open. Picture: JULIAN FINNEY/GETTY IMAGES

Tokyo — Japan celebrated Naomi Osaka’s victory over Serena Williams in the US Open final, with fans putting her stunning success down to focus and humility as much as her powerful performance at Flushing Meadows.

Osaka, the first Japanese player to clinch a Grand Slam singles title, was a picture of calm on Saturday in the midst of her opponent’s meltdown, which cast a pall over the final.

The 20-year-old, who was born in Japan but raised in the US, beat her childhood idol 6-2 6-4 on Saturday in a final marred by Williams’s outburst after she was handed a code violation for on-court coaching.

The runner-up also smashed her racket and verbally attacked the umpire for penalising her.

"Osaka played so well that Serena wasn’t able to play her tennis and she [Williams] got upset," said Mitsuko Sakai, 63-year-old amateur tennis player who woke up at 5am on Sunday in Tokyo to watch the final.

"She remained so calm throughout the match" despite the brouhaha, Sakai said. "I was very impressed by her mental strength. The entire audience seemed to be cheering for Serena, but Osaka concentrated on the game and won."

Prime Minister Shinzo Abe congratulated Osaka on Twitter and thanked her for "giving Japan a boost of inspiration at this time of hardship" — a likely reference to the earthquake that hit the northern island of Hokkaido on Thursday, killing at least 21 people.

Kei Nishikori, who lost in the men’s semifinals to Novak Djokovic and was runner-up in 2014, posted a video of Osaka lifting the US Open trophy on his Twitter page.

Japan has been charmed by Osaka’s off-court humility and genuineness as much as her on-court ferocity and that unpretentiousness came through in her post-match comments.

Standing on the podium waiting to be handed her trophy, Osaka heard only boos as an angry crowd took out their frustration on umpire Carols Ramos, whom they perceived as having been harsh on Williams.

"I know everyone was cheering for her and I’m sorry it had to end like this," said 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 "I’m really grateful I was able to play with you."

From Tokyo, 60-year-old tennis fan Kiyoshi Ogawa praised Osaka’s humility: "She tried to make all the attention go to Serena. That’s her beauty."

Tennis is nowhere near as popular as baseball, soccer or sumo in Japan, and the match was broadcast live only on the Wowow cable channel, not on any major television channel.

But as Osaka prepared to face Williams in Saturday’s final, local media began to contemplate what victory might mean.

The Yomiuri newspaper said: "The combination of her strength and childlike innocence is her charm," and hailed Osaka as "a new heroine Japan can be proud of".

Osaka, daughter of a Haitian father and Japanese mother, is helping break new ground in Japan as her identity challenges the country’s self-image as a racially homogenous society.

She is the latest biracial athlete in the limelight in Japan after sprinter Asuka Cambridge and baseball player Yu Darvish.

Osaka left Japan when she was three and was raised in New York and Florida.

She holds Japanese and American citizenship and speaks to fans on camera in broken Japanese — which has won over the public.