Flying in the face of popular opinion, Roach believes the fight happening five years after it was first floated, will actually benefit Pacquiao rather than Mayweather.
In an interview with ESPN Roach said: "Five years ago, maybe Floyd would've beaten Manny. [But] Manny has more heart right now.
"You really don't realize just how fast Manny is or how hard he hits until you actually get hit by him."
He added: "Floyd should enjoy being the A-side while he can because on May 2, Manny is going to put him on his backside."
Most pundits and fans have said that the five year delay of the fight will benefit Mayweather, as Pacquiao is believed to have lost much of the power that made him such a dangerous opponent.
The fight between two welterweights will take place at the MGM Grand Garden Arena in Las Vega on 2 May.