Serena Williams cried sexism after an extraordinary meltdown during her US Open final defeat by Naomi Osaka.

The headlines were supposed to be about Williams’ bid for a record-equalling 24th grand slam title and Osaka trying to become Japan’s first slam winner, but instead an argument with umpire Carlos Ramos that escalated dominated the match.

Williams was furious when she was given a coaching violation early in the second set after a hand gesture from her coach Patrick Mouratoglou, telling Ramos she would rather lose than cheat.

She was then docked a point for a second violation when she smashed her racket after dropping serve at 3-3. Continuing her argument with Ramos at the change of ends, Williams accused him of being a thief for taking a point away from her.

Ramos gave her a third violation, which resulted in a game penalty, putting Osaka 5-3 ahead. A tearful Williams argued her case with tournament officials but, although she held serve in the next game, Osaka served out the victory 6-2 6-4.

You can see the full 'thief' exchange in the video below as Williams became increasingly angry emotional at Ramos before eventually calling for the match referee.

It didn't change anything though and Williams went on to lose the second set shortly after.

Asked in her press conference what she would have done differently in hindsight, Williams became increasingly emotional as she said: “I can’t sit here and say I wouldn’t say he’s a thief, because I thought he took a game from me.

“But I’ve seen other men call other umpires several things. I’m here fighting for women’s rights and for women’s equality and for all kinds of stuff. For me to say ‘thief’ and for him to take a game, it made me feel like it was a sexist remark. He’s never taken a game from a man because they said ‘thief’. It blows my mind.

“I just feel like the fact that I have to go through this is just an example for the next person that has emotions, and that wants to express themselves, and wants to be a strong woman.

“They’re going to be allowed to do that because of today. Maybe it didn’t work out for me, but it’s going to work out for the next person.”

Mouratoglou admitted to ESPN that he was sending Williams a signal, but claimed every coach does it.

Responding, Williams said: “I literally just heard that too. I just texted Patrick because we don’t have signals, we’ve never discussed signals. I want to clarify myself what he’s talking about. I wasn’t being coached.”

What a baptism this was at the highest level for 20-year-old Osaka, who was up against Williams’ 30 grand slam finals and years of experience but was the one who kept her cool.

Williams was initially rattled in the first set by the quality of play from Osaka, who seemed to have no problem dealing with her opponent’s power and had the sharper movement and serve.

While all the drama happened around her, Osaka somehow maintained her composure, sitting at the final change of ends with a towel over her head to block everything out.

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.

The start of the presentation ceremony was also held up because of booing from the crowd and Osaka stood on the podium in tears.

Williams accepted it was an unfortunate position for Osaka to be put in, and said: “That’s why I said (during the ceremony), ‘I don’t want to answer the questions. This is her moment. Stop booing because she doesn’t deserve it. I don’t deserve it’. She played an amazing match. She deserved credit, she deserved to win.

It is not the first time the 36-year-old has run into trouble with officials at Flushing Meadows. In a semi-final against Kim Clijsters in 2009, she was penalised for threatening a line judge and put on a two-year probation.

Two years later, during a final loss to Sam Stosur, Williams called umpire Eva Asderaki “a hater” and “unattractive inside” for calling a hindrance penalty against her and was fined.

In a statement, the WTA said: “There are matters that need to be looked into that took place during the match. For tonight, it is time to celebrate these two amazing players, both of whom have great integrity. Naomi is a deserving champion and Serena at all times plays with class and makes us proud.”

A tearful Osaka told the crowd: “I know everyone was cheering for her and I’m sorry it had to end like this. It was always my dream to play Serena in the US Open finals. I’m really glad I was able to do that.”