'I'm honest, I was coaching' - Serena's coach Patrick Mouratoglou

With Osaka in control of the match after taking the first set, Portuguese chair umpire Carlos Ramos sent Williams into a rage when he handed the 23-time Grand Slam champion a code violation in the second game of the second set after he spotted Mouratoglou making hand signals from the player's box.

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A furious Williams informed Ramos in strong terms after storming over to his chair:

"I don't cheat to win!" she said. "I'd rather lose... I'm just letting you know!"

She then launched a series of verbal attacks on Ramos, demanding an apology for his call on the coaching violation to accusing him of being "a liar" and "a thief for stealing a point from me".

Williams again informed umpire Ramos that she is not a cheat and did not receive coaching from Mouratoglou, even adding that she had a daughter so would not do that.

"You owe me an apology," she said. "I have NEVER cheated in my life. I have a daughter and I stand for what is right and I have NEVER cheated."

Ramos sent Williams into a further rage when he handed the 23-time Grand Slam champion a game penalty for the verbal abuse.

Mouratoglou later admitted that he was coaching but added that it was not uncommon and that his opposite number, Osaka's coach Sascha Bajin, was doing the same.

Osaka became Japan's first ever Grand Slam champion after she closed out the 6-2 6-4 with unbelievable composure.