An emphatic performance from 20-year-old Osaka, who was born in Japan but raised in the United States, saw her take the win in straight sets 6-2, 6-4 at Flushing Meadows in New York.

However, the first Grand Slam win in history from any Japanese player was largely overshadowed by a dramatic confrontation between 23-time Grand Slam champion Williams and umpire Carlos Ramos.

Williams - who was aiming to equal Margaret Court's record of 24 Grand Slam singles titles, was initially given a code violation when Ramos judged a gesture from her coach in the stands Patrick Mouratoglou to be illegal coaching.

In a dramatic outburst Williams remonstrated to the umpire, saying she had not received any tactics from Mouratoglou, telling the umpire she would "never cheat to win and would rather lose".

However, Mouratoglou himself later admitted he was coaching.

"Everybody does it," he said, though he did state his belief that 36-year-old Williams was not looking at the time and so did not benefit. 

At 3-2 in the second set Williams then received another code violation for smashing her racquet, meaning Osaka was awarded a point. 

An extraordinary rant followed from Williams at the next change of ends, during which she called Ramos a "liar".

"You will never be on a court of mine as long as you live," she said as the crowd, backing their icon, booed the umpire.

"When are you going to give me my apology? 

"Say you are sorry."

In response Ramos awarded Osaka the next game, giving her a 5-3 lead that proved unassailable.

After the match the American congratulated Osaka at the net but refused to shake the umpire's hand.

Boos directed at the US Open officials continued to ring out during the presentation ceremony with Osaka in tears.

"It was always my dream to play Serena in the US Open finals so I am really glad I was able to do that," she said in her post match speech, before almost dropping the trophy as she left the stage.

Not wishing to let the issue slide, Williams later accused the umpire, Ramos, of sexism, saying: "He's never taken a game from a man because they said 'thief'".

Though Williams largely stole the limelight, Osaka's performance was widely praised, with former world number one Brad Gilbert from the US calling her performance "tremendous".

The men's final between Martin Del Potro and Novak Djokovic will take place tomorrow.