SYDNEY — When Mike Tyson last fought 19 years ago, former Australian boxing champion Jeff Fenech was his trainer and probably saved his life.

Jeff Fenech threw a white towel into the ring before the start of the seventh round of the non-title bout, rescuing the former heavyweight champion from a beating he was receiving from unheralded journeyman Kevin McBride. It was June 11, 2005 at Washington D.C. and it was clear the one time “Baddest Man on the Planet,” had nothing left in his heart or his fists.

The youngest man ever to win the heavyweight championship announced his retirement that night, presumably ending one of those most memorable careers in boxing history. That is why Mr. Fenech is shocked, yet supportive, that Mr. Tyson is returning to the ring two decades later, at age 58, to fight 27-year-old Jake Paul on November 15 at AT&T Stadium at Arlington, Texas.

“I definitely didn’t think something like this was going to happen,” Mr. Fenech told The New York Sun. “For me, my joy that night was being able to be there and make sure he never got hurt. I stopped the fight at the right time. I threw in the towel while other people were telling me not to. My priority was looking after my friend and the person I trained. Now I just hope he can get in there against Jake Paul and get it over and done with and show the world that at 58, he can be great again.”

That ugly night at Washington seems like a lifetime ago and in some ways it is. Mr. Tyson was a shell of himself when Mr. Fenech, who won world titles in three weight divisions, trained his friend for the fight against Mr. McBride. It would be Mr. Tyson’s third loss in four fights and the last in a record of 50 wins, 6 losses, 2 no contests and 44 knockouts. There were darker days ahead clouded by drugs, gluttony, the death of his daughter, and a loss of purpose.

“I won’t forget the day I was at one of his properties and he was on the lounge with a towel around him and chewing on chicken bones, looking like he was going to be dead soon,” Mr. Fenech said. “I walked outside, grabbed my wife, and started to cry. I told her, ‘I’m going to lose my beautiful friend.”

That is why Mr. Fenech says Mr. Tyson has won the battle even before he steps into the ring to fight Mr. Paul, a YouTube influencer, who is 10-1 as a boxer. After going from the “Baddest Man on the Planet,” to among “The Most Troubled,” Mr. Tyson began turning his life around more than a decade ago, appearing in movies, creating a one-man play that appeared on Broadway to being highly sought to make personal appearances throughout the world. Now he is set to make an estimated $20 million for a scheduled eight-round bout to be broadcast on Netflix.

“Beating Jake Paul is not anything great,” Mr. Fenech said. “But being 58 and doing what he has done and changing his body and changing his mind has been one of the most remarkable stories that I’ve ever heard. Can you tell me anyone who has been through what he’s been through and come out of the other side? Well, maybe Donald Trump. But what Mike has gone through has been amazing and where he is today is even more amazing.”

Mr. Fenech, 60, said he spoke with Mr. Tyson last week and gave him a game plan for how to win the fight. “I told him you’ve got to be smart,” Mr. Fenech said. “You’ve got to outthink him. Don’t try to show you’re the big, tough Mike Tyson because at 58 you’re not.”

Mr. Fenech advised Mr. Tyson to wait for Mr. Paul to throw a punch and then counter with his own power shots. “Don’t try to punch him at the same time,” Mr. Fenech said. “Concentrate on trying to make that punch miss and then make him pay. Jake Paul has worked hard, but Jake Paul can’t take Mike’s power. Even at 58 that’s one thing you don’t lose. If you’re in the right position at the right time and you land a punch it can be over. At 58, can Mike do that? I believe he can.”

Mr. Fenech did caution, the longer the fight goes on, the more problematic it could get for Mr. Tyson. “It hurts getting hit at 58. That’s why Mike’s got to get it over and done with ASAP,” Mr. Fenech said. “If Mike can land one good punch it will be over.”