Manny Pacquiao is one of the mellowest, most personable superstars in boxing - or any other sport, for that matter.

It takes a lot to rile him. But when things go sideways and cause him to fan the inner flames that have made him an eight-time world champion, watch out.

On Thursday, relayed through trainer Freddie Roach, Pacquiao delivered a crystal-clear message to Brandon Rios, the former WBA lightweight champ who he is fighting for the WBO international welterweight belt on Sunday at the Venetian Resort & Casino: no more Mr Nice Guy.

A day after Roach was embroiled in a confrontation with Rios' cornermen, the Hall of Fame trainer confirmed his fighter told him that he would "punish" Rios as payback for the American's conditioning coach kicking Roach and mocking his speech, which is affected by Parkinson's disease.

"Manny watched the video of what happened, then he asked me, 'Are those the guys who made fun of you?' When I answered yes, he said that was all he needed to know," said Roach. "Then he said he is going to punish Rios by taking him out quickly."

To be clear, Rios - who is also a nice guy - had nothing to do with the argument over use of the training ring. He was skipping rope several meters away when Roach got in the face of Alex Ariza, who responded by kicking him and making several loud references to his affliction.

Even though Pacquiao (54-5-2, 38 KOs) has lost his past two fights and has not stopped an opponent since Miguel Cotto four years ago, Roach is convinced the fired-up Filipino will come out throwing bombs on Sunday.

"This is his first fight in almost a year, and we are coming out of the best training camp we have ever had," said the trainer. "Manny is like a racehorse; he is very anxious to get back in the ring and prove to the world he is still an elite fighter.

"The best way to do that is to knock Rios cold. Manny knows that. Rios is a tough kid, but toughness doesn't win fights - boxing skill does. Initially, I didn't think this would go six rounds, but now, after the way Manny has prepared himself and all the other (things) that have happened, I don't think it will go four.

"Manny's hand speed and combinations will do all the damage, because he won't have to look for Rios. Brandon will stand right in front of him, and that is our big advantage because Manny is such a beautiful counter-puncher."

Like Pacquiao, Rios (31-1-1, 22 KOs) is coming off a loss in his last fight: a 12-round decision to Mike Alvarado in March. But the crowd-pleasing brawler from Oxnard, California, isn't wasting any energy thinking about the past.

"To everyone who thinks I'm just an opponent, a human punching bag for the great Manny Pacquiao, don't tune in late on Sunday," Rios said.

"This is my time, and I am going to make history for being the guy who retires Pacquiao. I'm younger, stronger ... and I hit harder than anyone he has ever fought so, yeah, I hope they keep disrespecting me.

"Is Manny talking about payback? My payback will come when I knock him colder than (Juan Manuel) Marquez did last year."

So there you have it: enough insult and intrigue to potentially morph an otherwise ordinary title fight for a minor belt into a brawl for the ages.

But don't hold your breath.

It says here (at the casino) that Roach's prediction is just about bang on the money, with Pacquiao scoring a relatively quick - and violent - knockout. Look for it in Round 5.

For his time and trouble, Pacquiao is guaranteed $18 million - which could inflate to north of $30 million once pay-per-view revenue is tabulated. Rios is guaranteed $4 million.

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