Billie Jean King Thanks Serena Williams for Calling Out Sexist Tennis 'Double Standard'

Billie Jean King and Serena Williams

The champion athlete tweeted her dismay over how the U.S. Open women's final unfolded.

One female tennis great has spoken out in support of another in the wake of a controversy-filled U.S. Open women's final.

Bille Jean King tweeted Saturday about the tense encounters that unfolded between Serena Williams and an umpire in the New York City tennis center that bears her name.

"Several things went very wrong during the @usopen Women’s Finals today," the 39-time Grand Slam title holder wrote. "Coaching on every point should be allowed in tennis. It isn’t, and as a result, a player was penalized for the actions of her coach. This should not happen."

During the dramatic match that she ultimately lost to upstart Naomi Osaka, Williams was penalized after chair umpire Carlos Ramos issued a warning for a code violation for receiving coaching, which is banned in Grand Slams.

After she was slapped with a second violation for racket abuse, Williams lost a point. She was penalized once again after calling the umpire a thief.

The penalty lost Williams the title. 

Following the match, Williams complained to reporters that the umpire's ruling was outright sexist.

"I've seen other men call other umpires several things and I'm here fighting for women's rights and women's equality and all kinds of stuff, but for me to say 'thief' and for him to take a game? It made me feel like it was a sexist remark ," she said, per CBS News.  "I mean, he's never taken a game from a man because he said thief. For me, it blows my mind."

In a second tweet on Saturday, Williams' trailblazing forebearer agreed.

"When a woman is emotional, she’s 'hysterical' and she’s penalized for it," wrote King. "When a man does the same, he’s “outspoken” & and there are no repercussions. Thank you, @serenawilliams, for calling out this double standard. More voices are needed to do the same."

Saturday's defeat comes at the heels of Williams' remarkable return to the game after the birth of her daughter, Alexis

From her loss comes a major win for 20-year-old Osaka, a New York-raised Haitian-Japanese woman whose rise she herself says would never have happened if it weren't for her "idol" Serena Williams.

Osaka was tearful despite having won the match and remarked she was "sorry it had to end like this."