Nobody better understands the problem Pacquiao will face on Saturday at the MGM Grand Garden when he meets Marquez for a fourth time than "Jesse" James Leija.
Leija, the former super featherweight champion, faced Hall of Famer Azumah Nelson four times over a nearly five-year period, winning a unanimous decision in their last bout in 1998 to win the series 2-1-1.
As Leija went through his preparations for that fight, he was flummoxed at times. Leija understood he needed to change tactics, because after having been in the ring with the man known in boxing circles as "The Professor," for 30 rounds at that point, Nelson knew Leija extensively.
Leija, too, knew pretty much what Nelson was going to do by the way Nelson positioned his hands, by the steps Nelson would take in the ring, by the feints he would use. It became, in essence, a stalemate.
"Some people have this perception that it's easier when you've fought the same guy over and over, but they're wrong," Leija said. "It's more difficult; way more difficult. I knew what he had and what he liked to do, but he knew what I had and what I liked to do.
"You take Pacquiao and Marquez, these guys are the best fighters in the world. If you're Manny, say, and you want to finally get that decisive victory he's been looking for, what can he do differently that Marquez hasn't seen before?"
Pacquiao and Marquez will become the 13th pair of boxers to have fought each other four or more times in their Saturday pay-per-view bout. In the last 40 years, it has only happened three other times.
Bobby Chacon and Rafael "Bazooka" Limon fought four times between 1972-85. Nelson and Leija met four times between 1993-98. Israel Vazquez and Rafael Marquez, Juan Manuel's younger brother, met four times between 2007-10.
The Vazquez-Rafael Marquez rivalry was compressed into a very short time frame. They first met on March 3, 2007, in Carson Their third bout was less than a year later, also in Carson on March 1, 2008.
All three were physical, brutal affairs which sapped a significant amount from each man. Having to fight three hard fights in such close proximity took its toll.
"I knew him so well and he knew me, because we didn't have a lot of time [between the first three fights]," Vazquez said. "By the time we got to the third fight, it was all about who was in the best condition and who wanted it the most."
Their fourth fight was 22 months after their third. From start to finish, they had 1,177 days in their rivalry. The Nelson-Leija series was contested over a four-year, 10-month span that was 1,776 days. But on Saturday, it will have been eight years, seven months and 3,137 days since the first time Pacquiao and Juan Manuel Marquez faced each other.
The fights were remarkably close and compelling, with Pacquiao usually on the attack and Marquez countering him expertly.
Leija said Marquez is the second-best counter puncher in boxing behind Floyd Mayweather Jr., but he also said Marquez may be the sport's best technical fighter.
"He's by far one of the best technicians in the game, even better than Mayweather, and to tell you the truth, he may be the best," Leija said. "Mayweather is faster, bigger and stronger. He's got great defence and he can make you miss, and, with that speed of his, he takes advantage when you do.
"But if you want to show someone how to box, teach them how to be a pure boxer, you'd show them Marquez. Not everyone can be as fast as Mayweather and not everyone can have the defence that Mayweather has. But if you study technique and work on that, you can become a great boxer like Marquez."
Marquez has used that technique to great advantage in their three fights. Pacquiao has been the faster, stronger man and has put Marquez down four times.
Three of those knockdowns came in the first round of the first fight in 2004. Had referee Joe Cortez stopped the bout after that third knockdown, as often happens, there wouldn't have been a second fight, let alone a fourth.
But Cortez's decision gave boxing fans the gift of three sensational bouts and allowed Pacquiao and Marquez to become intimately familiar with their own – and their opponent's – strengths and weaknesses.
"He is a good counter puncher," Pacquiao said of Marquez. "He is very patient and sits back and waits for action. If I waited for him to throw the punches first, the fight would be boring. That's why I have always been the one to make the fight between us."
Both have vowed to be more aggressive in the fourth bout, and Pacquiao trainer Freddie Roach has insisted that because of the controversy regarding the scoring in the first three fights, the judges may exhibit a subtle bias toward Marquez.
"I've said this a lot and I've talked about it with Manny, but I feel like when the bell rings to start that fight, we're already going to be down three rounds in the eyes of the judges," Roach said. "They know each other so well that it's tough to really be too much different, but I think from our standpoint, Manny needs to be more aggressive and show that killer instinct he had when he was a younger fighter."
Saturday's fight figures to be the last between them. Marquez is now 39 and logic suggests he doesn't have much more time left in the sport. Pacquiao is 33, but he's a Congressman in the Philippines and his political career is burgeoning. He's probably going to be around for another 18 months, at most.
Both men desperately want a decisive win, but given the nature of the first three, it's unlikely they'll get their wish. So, even though it wouldn't seem to make sense for a fifth one, don't totally rule it out if Pacquiao-Marquez IV is as compelling as I, II and III.
"It's hard to imagine a fourth one," Pacquiao said, jokingly, when asked if he could imagine a fifth fight with Marquez.
Promoter Bob Arum, though, wouldn't close the door on the possibility.
"There is a possibility," Arum said. "[It's] not likely, but a possibility. [Sugar Ray] Robinson and [Jake] LaMotta fought six times."
The Pacquiao-Marquez rivalry is one for the ages. Years from now, historians will be debating their bouts. Leija, though, assumes he knows what they're thinking.
"You just don't want to see the guy [in the ring] again and you want to be done with it," Leija said. "It's like, 'Please, get me someone else; anyone else.' I fought 42 rounds with Azumah and every one of those 42 rounds were brutal. When that fourth fight was over, I was definitely ready to see someone else and I would bet you they'll say the same thing [after the fight Saturday]."
- Sports & Recreation