Serena Williams was losing, so she decided to cheat. When she was caught and issued a warning, she threw a fit and cried foul. “I’ve never cheated in my life,” she yelled at Carlos Ramos, the Chair umpire.

Of course, that was a complete lie.

Her coach was giving her hand signals and admitted it after the match. But even after being caught cheating, the umpire issued only a warning. Serena should have quit while she was ahead. Instead, she broke her racquet, was cited a second code violation.

Williams went on a verbal rampage, berating and belittling Ramos: “You are a liar. You will never be on a court of mine as long as you live. When are you going to give me an apology? Say you are sorry!”

This is when Ramos issued a third code violation for verbal abuse, awarding a game to Osaka, who went on to win the match. Williams was fined $17,000 for her violations, and accused the umpire of sexism.

In the post match press conference, Williams cried foul as she claimed to be fighting for “women’s rights and for women’s equality and for all kinds of stuff.”

This is yet another example of a powerful, influential athlete acting like a 2-year-old. Williams was wrong on all counts, which is why she was both penalized and fined. Instead of behaving like a champion, she opted to be a spoiled brat. Instead of taking responsibility for her behavior, she denied and rationalized it.

The International Tennis Federation, the games-governing body, issued a statement saying that Ramos’ decisions “were in accordance with the relevant rules.” After Ramos was accused of sexism for handing out code violations that critics say he wouldn’t have given a man, the ITF said: “Carlos Ramos is one of the most experienced and respected umpires in tennis. Mr. Ramos’ decisions were in accordance with the relevant rules and were reaffirmed by the US Open’s decision to fine Serena Williams for the three offenses.”

Case closed. There will be no appeal because Williams knows she was wrong. In the meantime, she accused a good man doing a thankless job of being a liar, threatened to ban him from her future matches and pushed herself into the spotlight robbing the first Japanese US Open champion of the celebration she earned .

But this story gets even uglier. The Women’s Tennis Association and the U.S. Tennis Association have both come out in support of Williams. Katrina Adams, the president of the USTA who was also my mixed doubles partner in junior competition back in the late ’70s, praised Williams for her “sportsmanship and class.”

Apparently, it’s OK to cheat, so long as you don’t get caught; and it’s sportsmanlike and classy to break your racquet and berate an official. As long as you’ve won 23 grand slam titles, that is.

Is this the message that we want to send to our kids? Is this where tennis, a sport celebrated for its usually high-level conduct, is headed?

It’s one thing for an athlete to act out and be penalized. It happens all too frequently. But when powerful professional organizations and their leaders defend thuggish behavior, something has gone very, very wrong.

Serena Williams’ behavior was bad enough, but the WTA and USTA are far more influential. Their endorsement of her cheating and abusive conduct is despicable, and they owe all of us an apology.

Steve Siebold is a former professional tennis player who was ranked in the top 500 players in the world. He is author of “177 Mental Toughness Secrets of The World Class.” Online: mentaltoughnesssecrets.net