The spirit of Manny Pacquiao is the secret weapon powering George Kambosos' bold bid for Australian boxing immortality in New York.
Kambosos has revealed how three brutal but beautiful years serving as Pacquiao's chief sparring partner in the Philippines have steeled him for Sunday's unified super-fight with world lightweight champion Teofima Lopez.
Regarded as one of the all-time greats of boxing, Pacquiao is the only eight-division world champion in history and has won 12 major world titles.
He was the first boxer to claim the lineal championship in five different weight classes, the first to win major world titles in four of the eight "glamour divisions" - flyweight, featherweight, lightweight and welterweight.
The now Honourable Senator of the Philippines is also the only boxer to hold world championships across four decades - the 1990s, 2000s, 2010s and 2020s.
And Kambosos lived, breathed, sweated and fought with the legend for much of 2017, 2018 and 2019 before graduating from the ultimate boxing apprenticeship to earn his own shot at the IBF, WBA and WBO titles.
"I was with the great Pacquiao for 250 rounds, three world title campaigns and it was a fantastic experience to be under him," Kambosos told AAP from New York.
"Sparring him, you learn things that people would die to learn."
The chance of a lifetime to work with the master came in 2017 when Kambosos was preparing at the famous Wild Card gym in Los Angeles for his all-Australian showdown with Qamil Balla.
Kambosos caught the eye of Pacquiao's trainer Freddie Roach while going toe to toe with two of Pacquiao's ex-sparring partners and fellow former world champions Ray Beltran and Jose Ramirez.
"I was doing my thing in the ring and at that same time Manny had just signed to fight Jeff Horn," Kambosos recalled.
"Freddie Roach saw my style and he loved the speed and the movement and thought, 'you know what, he reminds me of Pacquiao himself'.
"He thought I would sharpen up Manny and said: 'how would you like to come out to the Philippines to spar Pacquiao?'
"I literally jumped straight at it. He said, 'he's fighting the Aussie guy, Jeff Horn'. I said it doesn't matter, I'll be there. This is the opportunity of a lifetime."
One that offered up endless other opportunities for a wide-eyed Kambosos, now 28 and with a 19-0 record in the pro ranks.
"Twice I got to fight on his undercard, which was great. I got to fight in Kuala Lumpur and in Las Vegas at the MGM Grand," Kambosos said.
"Because for those three years literally I was with Pacquiao as his main sparring partner; inside those ropes with him, running the hard miles in the Philippines in the heat over there with him.
"Everything he was doing in the heat, he was doing to prepare for his 12-round fights and I was doing.
"So that experience right there is invaluable for what I'm going to do this weekend."
His time with Pacquiao wasn't only physically testing, but mentally challenging as well being isolated from his young family.
"I would come over for the 10, 12-week camps and then go back home to be with my wife and at that stage my little daughter," Kambosos said.
"I had to sacrifice a lot in a third-world country - that's very dangerous as well - to make it to the top end and open up these doors and eventually they did open up and that's how I'm here right now."