By Robert Morales

BEVERLY HILLS - If there's one thing about Manny Pacquiao, he doesn't like it when people aren't happy with one of his fights. Juan Manuel Marquez doesn't like the idea that in his mind he has not received a fair shake in three fights with Pacquiao. Mix it all together, and the ingredients were there for a fourth fight.

It was formally announced Monday at a news conference at the Beverly Hills Hotel. They will tangle Dec. 8 in the welterweight main event at MGM Grand in Las Vegas (on HBO pay-per-view).

In their first fight in 2004, Marquez got up from three first-round knockdowns to earn a draw. In their second fight in 2008, Pacquiao (54-4-2, 38 KOs) won a split decision; Marquez thought he won. Their third fight last November ended in a majority decision for Pacquiao. It was their most controversial, as most reporters thought Marquez won.

Freddie Roach, Pacquiao's trainer, didn't say he thinks his man lost the third fight with Marquez, but it sounded like he knew Marquez fought very well and that he realizes he and Pacquiao will have to make some changes.

"I've had three chances to come up with the strategy and the style to beat this guy and we haven't done well in any of them and the last one was the worst. Marquez put the muscle on and he kind of landed the power shots in that fight," Roach said. "And a lot of people thought we lost that fight.

"But I need to get Manny to get that killer instinct back ... To be pound-for-pound the best fighter in the world, I think we need to knock this guy out. I don't think we'll win a decision regardless of how the fight goes."