The Women's Tennis Association (WTA) has backed up Serena Williams' claim of sexism in the way she was treated by umpire Carlos Ramos during her defeat in the US Open final.

The United States Tennis Association (USTA) also claimed that there are double standards in terms of how umpires treat women and men.

During Saturday's match, Williams was warned for coaching, then docked a point for smashing a racket before Ramos penalised her a game after she called him a liar and a thief.

The 23-time grand slam winner lost the match to Japan's Naomi Osaka who won 6-2 6-4.

Naomi Osaka beat Serena Williams, winning 6-2 6-4. Credit: AP

Williams argued on court with tournament officials, claiming she was being treated differently to how a man would be in such circumstances, a theme she continued in her press conference following match.

On Sunday, WTA chief executive Steve Simon said the match "brought to the forefront the question of whether different standards are applied to men and women in the officiating of matches.

"The WTA believes that there should be no difference in the standards of tolerance provided to the emotions expressed by men v women and is committed to working with the sport to ensure that all players are treated the same.

"We do not believe that this was done."

Simon also called for coaching to be allowed during grand slam matches.

Williams was docked a point for smashing a racket. Credit: AP

The USTA, which runs the tournament, agreed that there are double standards in terms of how umpires treat women and men.

USTA President Katrina Adams said: "We watch the guys do this all the time, they're badgering the umpire on the changeovers, nothing happens.

"There's no equality.

"I think there has to be some consistency across the board...

"We have to treat each other fairly and the same.

"I know what Serena did and her behaviour was not welcome, a line could have been drawn, but when you look at Carlos in this situation, it's a judgement call to give that last penalty because she called him a thief. They've been called a lot more.

"(He could have said), 'Hey, we're getting out of hand here, let's tone it down'.

"I think he would have (said that to a male player), I think it's a bond that they have and the way they communicate, and maybe not understanding they can have that same conversation with the women."

Winner of the men's event, Novak Djokovic, said that while he had sympathy for Williams in terms of the sanctions she was given, he did not agree that women are treated differently to men.

Williams was fined £13,000 including £7,700 for verbal abuse, however, she earned £1.43 million for reaching grand slam final.