Japan celebrated Naomi Osaka’s victory over Serena Williams in the U.S. Open final on Saturday, with fans putting her stunning success down to a steely focus and humble attitude as much as her powerful performance at Flushing Meadows.

Osaka, who became the first Japanese woman to clinch a Grand Slam singles title, was a picture of calm in the midst of her opponent’s meltdown that cast a pall over the final.

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

The runner-up also smashed her racket and verbally attacked the umpire for penalizing 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 5 a.m. 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 cheering for Serena but Osaka concentrated on the game and won.”

Prime Minister Shinzo Abe congratulated Osaka on Twitter, thanking 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.