By Mark Lamport-Stokes
While eight-times world champion Pacquiao has been installed as an odds-on favorite by Las Vegas bookmakers for the scheduled 12-round bout, Roach believes his fighter's strategy during the first five rounds will be decisive.
"If Manny makes the mistake of attacking Shane without setting it up first, he will walk into a counter-shot," Roach told reporters at the MGM Grand on Thursday. "That's my biggest concern.
"When Shane is on the ropes trying to set up the counter-shot, Manny knows the move to make. He does it to me every day."
Asked what Pacquiao's response should be, Roach replied: "Get him off track, get him all mixed up.
"He knows what to do when the guy is trying to sucker him into a counter-shot, and that is what Shane is going to do. That's part of his game plan. He'll counterpunch the hell out of you and he has knockout power.
"The first five rounds of this fight are very critical. The way we go about attacking Shane is going to have a lot of thought behind it. If you just walk into Shane and attack him you just walk into the fire."
American Mosley, a four-times world champion in three weight divisions, is bigger and taller than Pacquiao. According to Roach, he also possesses the most lethal punch the Filipino has ever faced.
"He's probably not the best puncher we've ever had but he's got the best speed, and speed is power," said Roach.
Asked if Mosley was likely to be the hardest one-punch boxer Pacquiao had ever faced, Roach replied bluntly: "Yes."
Southpaw Pacquiao, who has a glittering career record of 52-3-2 with 38 knockouts, has never trained harder for a fight, according to Roach.
"It's the best training camp we've ever had and I think Manny is in the best shape ever," the shrewd, bespectacled trainer said. "If Mosley brings his best, we're ready for his best.
"I don't think there is any room for an upset, but in boxing you never know. We're 100 percent ready on our end. We've done everything we can to get ready for the fight."
Mosley (46-6-1, 39 KOs) is three-and-a-half inches taller than Pacquiao and holds a reach advantage of seven-and-a-half inches.
Although the 39-year-old American is in the twilight of his impressive career, the Pacquiao camp is not under-estimating the threat posed by a boxer who once held the mythical tag of being the best pound-for-pound fighter.
"Cotto fought the best fight of his life," Roach recalled. "Cotto out-boxed Shane, and Shane had trouble with boxing. He loves guys that come to him and he sets up guys all the time.
"If you box Shane in, then you're going to give him problems and he has trouble with speed. He has speed but he has trouble with speed also.
"It's seeing the punches coming at you, that's the thing," he added of the veteran Mosley. "With age, fighters don't get out of the way like they used to."
(Editing by Frank Pingue)