Chris Evert, a former top tennis player, tweeted that Ramos should have warned Williams about the verbal abuse violation before penalizing her.

Andy Roddick, who retired from the sport in 2012, wrote on Twitter during the game, “Worst refereeing I’ve ever seen ...... the worst !!!”

James Blake, a retired tennis star, tweeted that he had said worse things on the court and did not get penalized. “And I’ve also been given a ‘soft warning’ by the ump where they tell you knock it off or I will have to give you a violation,” he wrote. “He should have at least given her that courtesy. Sad to mar a well played final that way.”

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Billie Jean King, a tennis legend and a pioneer for women in the sport, congratulated Osaka in a tweet before thanking Williams in a separate one for calling out a double standard between men and women in the sport. “When a woman is emotional, she’s ‘hysterical’ and she’s penalized for it. When a man does the same, he’s ‘outspoken’ & and there are no repercussions. Thank you, @serenawilliams, for calling out this double standard. More voices are needed to do the same.“

Actor Reese Witherspoon and TV host Ellen DeGeneres thanked Williams on Twitter for standing up for women’s rights. Actress Gabrielle Union called her “the best athlete the world has ever seen” and said Osaka demonstrated “#BlackGirlMagic & fierce determination.”

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Serena Williams of the U.S. makes her case to Brian Earley and Donna Kelso, left, during the U.S. Open women's singles final against Naomi Osaka of Japan at Arthur Ashe Stadium in New York, Sept. 8, 2018.

BEN SOLOMON/The New York Times News Service