It was the only sign of an “apology” from Serena Williams. Ten months after the ugliest match in U.S. Open history, Williams admitted she sought a psychologist.

Her temper tantrum against umpire Carlos Ramos in the 2018 U.S. Open finals against Naomi Osaka wasn’t her first blowup in Flushing Meadows. How could a player with so much success and fame be so angry?

Rick Macci, Williams’ first coach, wrote the book, “Macci Magic: Extracting Greatness from Yourself and Others.” He admitted Williams could have more Grand Slams with more mental control and said he feels Osaka caused her explosion — not Ramos.

“She has the talent to keep on rolling and win five more Grand Slams,’’ Macci told The Post. “I feel every match she plays is in her hands. I looked at [the match] through a different lens. Osaka deserved to win. She served as well and counterpunched Serena’s best shot with quality. She became a little edgy. Even great players, when not super-comfortable, anything can happen. It was a combination of how her opponent played that caused Serena to be more combative and voice her opinion. It was more about Osaka.’’

Williams poured her heart out in August’s Harper’s Bazaar, an essay billed as an apology. But it was hardly an apology for the misbehavior against Ramos — histrionics that endured almost an entire set and through three code violations.

The only apology went to Osaka for ruining her moment. Williams came off as a tortured soul, writing, “I still couldn’t find peace.’’

“This debacle ruined something that should have been amazing and historic,’’ Williams penned. “My heart broke. I started to think again, ‘What could I have done better? Was I wrong to stand up? Why is it that when women get passionate, they’re labeled emotional, crazy, and irrational, but when men do they’re seen as passionate and strong?’”

Williams is back at the scene of the crime — under the lights Monday at Ashe Stadium for a first-round match against Maria Sharapova.

And Williams carries in more baggage. Her anger-management travails at the Open date to 2004. No lessons seemed to have been learned.

In fact, in the documentary, “Backstory: Serena vs. The Umpire,” Williams’ current coach, Patrick Mouratoglou, called the night a positive.

“It was horrible for us and Serena,’’ the French coach said. “It was fantastic for tennis. That was the best moment in tennis in 10 years. You want passion.’’

Chris Evert, at courtside, said she thinks little of his statement.

“I don’t agree with that at all,’’ Evert said Friday. “Yes, it got a lot of exposure. So do other bad things that happen in the world. I don’t think it was good for tennis, the integrity of the game. I was down at the level presenting the trophy. It was thundering, it was vibrating, the floor vibrating, the boos deafening. I saw Naomi sobbing. That isn’t the greatest thing that’s ever happened in the sport.’’

In 2004, Williams’ Open volatility first flashed. She hit a clear winner called wide. Williams approached the chair umpire, a woman, and shouted repeatedly, “It was not out!” then bellowed, “Do I need to speak another language?”

That was tame compared to 2009’s Open semifinal against Kim Clijsters, when she exploded at a lineswoman after she called a foot fault. Brandishing her racket, Williams snapped, “I’m going to take this f—g ball and shove it down your f—g throat. You better be right.’’

The 2011 Open final against Samantha Stosur became another embarrassing moment after she screamed “C’mon” as she belted a winner. It was ruled a do-over.

“Aren’t you the one who screwed me over the last time?’’ she barked at the chair umpire, a woman. “Yeah, you are. You have it out for me. Not cool. This has happened to me too many times. It’s not fair.’’

Though those three incidents involved female judges, Williams turned last September’s fight into a women’s rights issue.

The 2018 fiasco began after Williams got pummeled in the first set, 6-2. Two games into the second set, Ramos issued a code violation — a warning. Ramos had spotted Mouratoglou pushing his thumbs forward.

Williams flipped, arguing she would never cheat. Repeatedly, she demanded an apology from Ramos. After the match, Mouratoglou admitted he was coaching, and he did so again in the documentary.

The fight escalated across the second set. Williams scolded Ramos: “Don’t talk to me.’’ Her second code violation for slamming a racquet cost her one point, then the night went off the rails.

During a changeover, Williams reprimanded Ramos: “You will never, ever be on a court with me as long as I live,” then called him “a liar” and “a thief.” Ramos issued the third violation for “verbal abuse,” costing Williams a game.

Good for the sport?

“Hopefully something good can come out of it ultimately because it was a lose-lose for the ref, Serena, tennis,’’ John McEnroe said Friday. “Naomi was obviously extremely upset. That was a bit of a train wreck.’’

Williams hasn’t won a title this year but has executed two magazine-cover shoots — for Harper’s and Sports Illustrated’s fashion issue.

She’s still “The Franchise’’ despite not having been a champ since becoming a mother to Alexis, now 23 months old.

“In a blink of an eye, if the right things are in her head, she can crush anyone like a grape,’’ Macci said.

Williams enters the Open after forfeiting an Aug. 11 match due to back spasms in Toronto. She then withdrew in Cincinnati, though she said her back spasms routinely last “24, 36 hours.”

“I never think she can’t win,” McEnroe said. “I’m not sure how injured she was in the first place. It’s hard for me, even though she hasn’t won an event since her kid, to think she’s not the favorite.”

Williams’ chase for the record-tying 24th Grand Slam continues at age 37. If she never gets there, how unfortunate would it be if part of Serena’s legacy was her temper.