For 12 rounds, or less, Saturday night,
Roach's challenge leading up to the fight in Las Vegas has been to device a plan to beat Mayweather (47-0, 26 knockouts) in what he sees as the culmination of his life's work.
"Yes, it's the biggest fight of my life," Roach, 55, said recently at his Wild Card Boxing Club in Hollywood. "I've been in big fights myself, trained for some big ones. Nothing's bigger than this."
The product of a Massachusetts home where his father raised his boys to fight, Roach was a pro fighter for eight years. After his last bout, in 1986, Roach shifted into training and has emerged as a seminal figure in the sport.
The seven-time trainer of the year not only accepts newcomers into his gym who want to pay $5 per workout, Roach travels globally and is so plugged-in socially that he counts CBS Chief Executive
Now, he'll usher Pacquiao to the sport's greatest stage.
Part of his prefight strategy is to aggravate Mayweather, who Roach has taken to calling "Mr. 47 and 1," while chastising the boxing knowledge of the opponent's father and trainer, Floyd Mayweather Sr.
"[Floyd Jr.] has been avoiding Manny for so long [because] he didn't want this fight," Roach said. "He can pretend it was a strategy to build up the fight's value, but that's not true.
"For once, Mayweather wasn't able to handpick his opponent. He was forced to take this fight by Manny, the media and the fans. His excuses for not making the fight haven't held water. ... Mayweather ran out of road. Mayweather may have been the 'A side' during the negotiations, but once he signed the contract he became the 'B side.' "
Verbal daggers, indeed.
"A win here is so essential to me," Roach said. "I've talked a lot, said a lot of things about Floyd. We have to win the fight. Have to. And I think we will."
For years Roach has been studying Mayweather's habits in the ring, hoping a Pacquiao fight would happen. He ticks off Mayweather's tendency to jab hard to the body, how his feints can set up a flush right to the face, how Mayweather's shoulder rolls protect his head and force an opponent to extend his reach and become vulnerable to counter punches.
"It's been difficult. The game plan of getting Manny to do the right things at the right times all the time is hard," Roach said.
Roach and Pacquiao teamed up 14 years ago and this will be their 31st fight together.
Roach believes Mayweather, 38, will transform from unbeatable to suspect against a fast left-hander like Pacquiao.
Long ago, when Roach took over Pacquiao's training, they added a strong right hand to go with Pacquiao's destructive left; the Filipino knocked out lightweight champion David Diaz with a right in 2008.
But for the Mayweather bout, Roach has pushed his fighter to make the left a key punch.
Roach, who fought as a lightweight for eight years, recalled how his former trainer, the late Hall of Fame cornerman Eddie Futch, once ordered him to eat left-handed until Roach felt ambidextrous.
So in training camp Roach told Pacquiao not to throw a single right hand in 12 rounds of a sparring session to prepare for Mayweather.
"It's an advantage for a southpaw to land that shot first, so we did it and [put] the footwork together, too," Roach said.
A stiff left by Pacquiao has ended fights and could very well change the course of the Mayweather bout.
In his last bout, Pacquiao produced a career-best six knockdowns of then-unbeaten Chris Algieri in November. Roach also believes that cutting off the ring can produce a victory against Mayweather.
Early in sparring sessions, however, Roach was so bothered by Pacquiao's erratic ability at cutting off the ring that he briefly considered hiring a sports psychologist, confiding to a reporter, "You think I'm over-thinking this?"
That day Roach waited for Pacquiao to finish an interview, then sat and talked to the welterweight champion.
"I was thinking about it, so I went in there and said, 'You know what? I'm going to be the sports psychologist right now and find out why he has difficulties doing things,' " Roach said.
And how would he describe Pacquiao's attention to the discipline now?
"Tremendous," Roach said.
"You learn more in defeat," Roach added. "You can always tell a fighter, 'You should've done this more, or that more,' and he can't say, 'Yeah, but I won.' "
The best adjustments in Pacquiao's career followed his loss to Erik Morales in 2005, and his knockout defeat to Juan Manuel Marquez in 2012, Roach said.
"Losing is not the worst thing in the world because it makes you better. I truly feel that," Roach said. "I won my first 10 fights, lost my 11th, then won 17 straight after that because I knew I needed to work harder after taking a more experienced guy lightly."
During his long hours in training camp at Wild Card, it has been easy for Roach's thoughts to wander.
He says he wishes he could have another conversation with Futch, who trained
Futch died in 2001, the year Pacquiao and Roach met.
"I would like to ask him his advice," Roach said of Futch. "I wish he was still around. ... Whenever I'd need help in big fights, I'd say, 'How do you think we should fight this fight?' He was really good at finding game plans to win. So I really, really wish Eddie was still here. I'd just ask him, 'How do we deal with this guy [Mayweather]?'
"I think I know what he would say, and that's what we're doing, but I don't know exactly."
Roach, and Pacquiao, will learn the answer Saturday night.