Serena Williams' bid for a 24th Grand Slam title imploded in a furious tirade against umpire Carlos Ramos, calling him a thief after he docked her a point for two code violations.
Osaka, 20, triumphed 6-2, 6-4 in the match marred by Williams's second set outburst, the American enraged by umpire Carlos Ramos's warning for receiving coaching from her box.
Her outburst then earned her a game penalty, prompting a further outburst to tournament officials and putting Osaka within one game of victory.
The altercation started when Williams smashed her racket to smithereens and Ramos gave her a code violation warning. Coupled with the prior coaching warning, this indicates she's given a point penalty.
Pausing the game, she went up to the umpire, telling him: "You owe me an apology."
"Every time I play here, I have problems. I did not have coaching, I don't cheat. You need to make an announcement. I have a daughter and I stand for what's right. You owe me an apology."
Ramos, however, remained poised but in a manner that showed his clear distaste towards Williams.
"For you to attack my character is wrong. You owe me an apology. You will never be on a court with me as long as you live. You are the liar. You owe me an apology. Say it. Say you're sorry.
"How dare you insinuate that I was cheating? You stole a point from me. You're a thief too.
"This is not right. It's because I'm a woman. This happens to me every time I play here. It's not right. It's not fair. I've worked so hard to be in this position."
Subsequently, Osaka got off a perfect start at 15-0 with only three points away from the title. Despite Williams levelling the game, her opponent managed to lead again with a service winner and following another one, secured her victory.
While Osaka was declared the 2018 US Open champion and Williams made a cursory embrace, the latter refused to shake Ramos' hand, telling him, again, he owed her "an apology".