There is a school of thought, zealously espoused by Mayweather, that if a champion is beaten in one fight it kills the legend forever.
Pacquiao is the living lie to such a theory. He lost twice in 2012 alone, first in a contentious split decision against Timothy Bradley and then in a savage sixth-round knockout by Juan Manuel Marquez.
But his public would not relinquish him so easily. A boxer who had been propelled from selling sugar doughnuts to gracing the cover of Time magazine under the headline "The Great Hope", would never be allowed to wither sadly into retirement.
This long-promised confrontation with Mayweather signifies an opportunity he had all but abandoned. All week he has been appearing in adverts for the US shoe company Foot Locker, in a series entitled It's Really Happening. "Floyd's going to fight me!" he cries, in a skit that plays upon his scampish good humour. Even though he is fighting for 65 million ($132 million), when he used to be happy with a couple of pesos for a street brawl, his essential exuberance has not changed. It is a trait likely to be borne out inside the ring tomorrow, as Mayweather's calculated defence contrasts with Pacquiao's whirlwind of attack.
Aptly, the day of the fight will be a public holiday for his 98 million compatriots. He can trust that the vast majority will be gathering around screens wherever they can be found.
At no stage has he ever been resented for his colossal fortune. Filipinos, on the contrary, appear united in his conviction that his humility is much more than skin-deep. He continues to send substantial donations home, channelling a benevolence that he would display in school days, handing out paper to friends who had forgotten theirs or who could not afford any. He is understood to have paid over 3 million so that every member of his 900-plus entourage can watch the Mayweather battle.
None of this is to imply that Pacquiao is unimpeachable. He is being pursued for 33 million in unpaid taxes, and was forced to deal with numerous allegations of gambling and infidelity before rescuing his relationship with his wife Jinkee. He credits the about-turn in his life to finding God, a tale that plays powerfully in the Philippines, an intensely devout Christian country.
In Gensan, the reminders of his distinction as the only eight-division champion in boxing history are even more prevalent. Businesses from gyms to water companies all carry the Pacquiao imprimatur. Even Princess, his 8-year-old daughter, has a printing company named after her.
Among his manifold talents, Pacquiao is feted as an accomplished singer in his native land. Two of his albums have gone platinum in the Philippines, and for this defining duel he has brought out a song especially, entitled Lalaban Ako Para Sa Pilipino, translated as "I will fight for the Filipinos".
"Even if I am in pain," he sings, "I force myself to hide it and be silent. My heart is bleeding, yet others don't see it, but what is important is that my country is happy. I will fight around the world, I will risk my life. I am Filipino, we are Filipino."
He could have contrived no more potent call to arms than this.
