A fierce competitor, she likely felt that she was robbed of a championship moment. There is disparity between the ATP men's tour and WTA women's tour; between Grand Slam tournaments and lower-level events; and even among the Slams themselves.
Serena Williams is given a code violation warning for coaching with the score at 2-6, 1-0, which she fiercely disputes. This should not happen.
Williams said the incident strengthened her belief that women players are treated differently to their male counterparts in the sport. "When a man does the same, he's 'outspoken" and there are no repercussions".
Like Williams, Osaka has enjoyed a sibling rivalry although nowhere near as intense as Serena and her sister Venus. "More voices are needed to do the same", she said.
Williams was handed multiple controversial penalties in the match, including one that cost her a game and put Osaka up, 5-3, in the second (and final) set.
At the next change of ends, Williams fumed, accusing Ramos of stealing a point from her.
Osaka made history on the track after 79 minutes of dominance over Williams, but their meeting will be diluted forever by the hostile scenes starring Serena, uncontrolled before the chair umpire, Carlos Ramos, whose only fault was to strictly comply the regulation and the ethical code. "I have a daughter and I stand for what's right". "He's never taken a game from a man because they said 'thief, '" Williams said.
Added Williams, with a laugh: "I really hope to continue to go and play here again".
"They're going to be allowed to do that because of today", she said.
During a press conference, Williams criticized the calls from Ramos as sexist. Then, in the same tournament, Mohamed Lahyani gets off the umpires' chair to talk to Nick Kyrgios and persuade him not to give up on a match.
What happened: In the opening game of the third set, Williams hit a backhand that landed in - and was ruled in by a line judge - but Alves awarded the point to Capriati.
"Ramos claimed he was just following the rules, but in actuality, men stretch the rules all the time and are lionized for being "bad boys" while women are benched".
"Ramos might not have been wrong, but that doesn't make it right", Bryan Armen Graham wrote.
The controversy dampened Osaka's victory, the first for a Japanese player, but Williams was quick to say during the post-match trophy presentation that her opponent deserved the win.
Neither Williams nor her vocal fans initially realised she had been given either the point or game penalty, and the boos and jeers on the second occasion were deafening.
In the second set's second game, Ramos warned Williams for getting coaching, which is against the rules in Grand Slam matches.
She resumed arguing with Ramos later, saying, "You stole a point from me. I don't cheat to win, I'd rather lose".
Celebrities and other athletes shared messages of support for both Ms Williams and Ms Osaka.
"You owe me an apology", she told him. She was then forced to forfeit an entire game.
After the call, Twitter lit up with reactions.
Prime Minister Shinzo Abe took to Instagram to praise Osaka's accomplishment.