She was reduced to tears after calling for an official in hopes to get Carlos Ramos' ruling overturned. "You stole a point from me and you are a thief", Williams said during a changeover at 3-4, to prompt the ruling.
Williams said she's going to continue to fight for women.
To her vast credit, Osaka held her nerve among the chaos to claim victory, after Williams had remonstrated emotionally with the tournament referee, insisting she had been unfairly treated.
"It doesn't really feel that real right now".
Asked if she would now think of her childhood idol differently, Osaka said: "I'm always going to remember the Serena that I love".
"This is a sport that gave us John McEnroe; the sport that gave us Ilie Năstase; Jimmy Connors; I could go on and on - men who have gotten away with far worse than saying 'You're a thief. No matter what happens in any match - semis, final - I feel like I've already won".
"He (Ramos) alleged that I was cheating, and I wasn't cheating", said Williams.
Serena Williams was going for her 24th grand slam title.
It was drama-filled conclusion to a final that was rich with storylines but will now go down as one of the most controversial Grand Slam finals of all time. Let's make this the best moment we can.
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Keys was not without chances after amassing 13 break point opportunities throughout but she was unable to convert any against the impenetrable 20th seed.
Sascha Bajin, who served as Williams' hitting coach from 2008-2015, has helped Osaka reach the top of her game in his first year as her coach.
"I got a little emotional out there because a year ago I was literally fighting for my life in the hospital", she said.
The 36-year-old Williams took umbrage with the statement, insisting that her coach simply gave her a thumbs up as a sign of support and encouragement.
Alison Hughes will become the second female umpire to chair a U.S Open men's singles final.
"Should they be allowed have an influence on the result of a match?" We don't have signals, we've never discussed signals.
However, the final was overshadowed by Williams receiving three code violations - coaching, racket abuse and verbal abuse - and eventually a game penalty on Arthur Ashe Stadium.
The tranquillity didn't last long.
Osaka spent the formative years of her childhood living in NY and first came to Flushing Meadows as a fan hoping to catch a glimpse of Williams. A second code violation came with a point penalty to start the next game that sent her into orbit. We'll get through it. Let's not boo anymore... I haven't cheated in my life.
"I do know for me one of the main things was that when I was practising with my dad, if my sister wasn't there, I don't think I would have made it".