By Mark Lamport-Stokes
However, Marquez has repeatedly claimed he won both contests and Pacquiao felt insulted after his opponent wore a T-shirt bearing the legend: "We Were Robbed" when their November 12 showdown in Las Vegas was promoted in the Philippines.
"I have never been so motivated as I am for this fight," Pacquiao told Reuters on Wednesday before sparring with his trainer Freddie Roach at the Wild Card Boxing Club. "I almost can't wait for the fight.
"I want to prove that he (Marquez) was wrong in wearing that T-shirt claiming he won the last two fights.
"So this is kind of a special fight, the most important fight in my boxing career, because I want this fight to be the answer to all the doubts that have been raised."
Asked if he had taken Marquez's claims personally, Pacquiao replied: "Right now, outside the ring, there is nothing personal but when I get into the ring on November 12 it's going to be personal for us."
Roach, who has worked with 31 world champions in his Wild Card gym on the outskirts of downtown Los Angeles, said he had never seen Pacquiao so fired up for a fight.
"He's motivated but he still won't talk about it," Roach told Reuters, referring to the baiting by Marquez. "I say to him: 'Manny, you don't like this guy?' And he just smiles at me. I let him enjoy it.
"When Marquez came out to the Philippines and wore that T-shirt, he embarrassed Manny a little bit. It was a slap in the face and I think Manny will pay him back."
Roach, a shrewd tactician who has been uncannily accurate with his fight predictions, forecast a Pacquiao victory inside the distance at the MGM Grand Garden Arena in Las Vegas.
"I don't think the fight's going to last six rounds," Roach said. "It's going to be a helluva fight until it ends because one thing about Marquez is that he will fight.
"They say he (Marquez) has put on a little bit of muscle and he is getting a little bigger upstairs. It looks like he might want to exchange with us and I hope that happens."
However, Roach felt the Mexican, a three-division world champion, would once again be the toughest opponent the Filipino has faced in his illustrious career.
"Manny loves it when guys come to him and they're aggressive," said Roach. "Marquez is a counter-puncher and we're probably going to have to go to him (Marquez) to make the fight happen.
"It's a little harder for Manny to do that and there is no question that Marquez has the most difficult style for us."
In that bout, as well in his previous two wins against Joshua Clottey and Antonio Margarito, the Filipino was criticized by many of his supporters for 'going soft' on his opponents in the late rounds.
On November 12, however, Pacquiao can be expected to go full throttle against Marquez, who recovered from three knockdowns in the opening round to earn a draw when they first clashed in May 2004.
Just ask any of Pacquiao's sparring partners who have come in for a pounding in recent weeks at the Wild Card gym.
"Manny has been a little rough on his sparring partners," Roach said with a smile. "But they try and hold him and they're doing a good job. Manny is a completely different animal to the guy that fought Marquez the first time."
(Editing by Greg Stutchbury)