Now, in preparation for his May 2 bout against
Pacquiao trainer Freddie Roach said he put the fighter through an extended session this week in which he could only punch with his left hand.
"We did 12 rounds of left hand only. The right hand was never used," Roach told The Times.
The lesson not only sharpened Pacquiao's use of the left, he said, it reinforced the trainer's teachings that the proper footwork can allow Pacquiao to hand Mayweather his first loss.
"It's about putting everything together," Roach said.
A week earlier, Roach had expressed concerns about Pacquiao's ability to cut off the ring against the elusive Mayweather. Now he assessed Pacquiao's competence with the discipline as "tremendous ... he knows exactly how to do it."
There's still the matter of executing the fight plan in the MGM ring, but Roach, preparing for his 31st bout with the Filipino star, said he's comforted by his past experience with Pacquiao taking a lesson and executing it.
In 2005, Pacquiao suffered a unanimous-decision loss to Erik Morales, and Roach apologized to Pacquiao afterward for not properly training him to use the right hand as a power punch.
In the next fight, a sixth-round stoppage of Hector Velasquez at Staples Center, the process was underway.
By 2008, in a move up in weight to take away the world lightweight belt from David Diaz by ninth-round technical knockout, it was perfected with a right-handed finish.
"Same routine, now the opposite side," Roach said of the current situation. "It's all about usage, muscle memory ... [Pacquiao and Mayweather] will be equal at some point [in the bout]. Manny's been favoring the right side so much now, I need to bring the left back."
And the left, obviously, is the southpaw's most brutal punch.
"Oh, it's deadly," said Roach, who has the welts from practice to prove it. "Deadly. My chest is ... killing me."