The two boxing superstars failed to agree terms for a fight five years ago, but they will finally meet in a Las Vegas clash on May 2.
Pacquiao appeared an unstoppable force at that stage in his career as he had cut a destructive path through the weight divisions.
He has since been beaten on points by Timothy Bradley and halted in shocking fashion by Juan Manuel Marquez, but these defeats have not diminished Roach’s confidence.
The Filipino???s long-term cornerman insists he has spotted signs of decline in Mayweather, despite the American???s 47-fight unbeaten record.
Roach told boxingscene.com: “Back in 2010, Manny was still growing into a welterweight. His first two welterweight fights were against Oscar De La Hoya in 2008 and Miguel Cotto in 2009 where he only weighed 142 and 144 pounds respectively, and in between he dropped down to 138 to fight Ricky Hatton.??
“Floyd has been campaigning as a welterweight since 2005 and weighed 150 in his fight against De La Hoya, so that might have given Floyd an advantage. I still like Manny’s chances in that fight, but I think the Manny of today has a lot more in his favour.
“In 2010, the two-year age difference between the fighters was not significant to either, but that???s not true today. Floyd at 38 is doing things he didn???t do in the past. Floyd is a defensive genius, but he has always depended on his legs to perform and you can see now that his legs do not have the same spring or fluidness of his early years.
“The 2015 version of Manny is more mature, smarter and less reckless than the 2010 version. He will be treating the ring like a chess board, anticipating Floyd’s moves – ready to cut him off and attack every time he creates an opening.”
While predicting the outcome of the ‘Fight of the Century’, Roach drew comparisons to Pacquiao???s convincing victory over another ring legend Oscar De La Hoya.
Pacquiao overwhelmed ‘The Golden Boy’ with his blistering hand speed, forcing De La Hoya to quit after the eighth round, and Roach expects a similar outcome.
“I look at this the same as I did when Manny fought Oscar De La Hoya. I have all the confidence in the world that Manny is going to knock Floyd out on May 2,” he said.