It's been only two days since Manny Pacquiao's historic 12th-round knockout of Miguel Cotto on Saturday night in Las Vegas to win a welterweight title -- Pacquiao's record seventh in a seventh division -- but already the focus is firmly on a potential Pacquiao showdown with Floyd Mayweather Jr.

And Freddie Roach, the trainer Pacquiao now refers to as "my master," is licking his chops for the fight after seeing Pacquiao cut through a big, strong welterweight like Cotto.

"I've thought about Mayweather for a long time now," Roach told ESPN.com from his Wild Card gym in Hollywood, Calif., on Monday. "He's the ultimate opponent. His style does pose some problems because he's very good at what he does. But after seeing Manny with Cotto, Manny showed he takes a punch well. We'll definitely knock Mayweather out. He'll break down. He can't stand up to Manny's pressure. He won't last as long as Cotto.

"I got a feeling Mayweather doesn't really want to fight Manny. When he says he wants 65 percent [of the revenue], that's like saying he doesn't want to fight," he said.

Roach had heard about Mayweather's first public comments about the possible mega-fight, which if made would almost certainly challenge the pay-per-view buy record of 2.4 million set by Mayweather's fight with Oscar De La Hoya in May 2007.

"The thing is with Pacquiao I don't see any versatility as a fighter," Mayweather, the former pound-for-pound king who ended a retirement by easily outpointing Juan Manuel Marquez on Sept. 19, said to England's Sky Sports. "He's a good puncher but just one-dimensional.

"I'm in a no-win situation. If I beat Manny Pacquiao you know what they are going to say? 'You are supposed to beat him, you are Floyd Mayweather, you are the bigger man.' If I knock him out they'll say, 'You're supposed to knock him out [because] he's been knocked out before.' I'm in a no-win situation and when I beat him no one is going to be surprised because he's been beaten before. Whatever I do to Pacquiao has been done before. He's been beaten on three occasions. And if I knock him out I don't want the world shouting because he's been knocked out twice before [as a flyweight in the 1990s]," he said.

Roach isn't buying Mayweather's talk, especially considering Pacquiao is obviously a far superior fighter now than he was during his days as a flyweight, when he was weight drained and was stopped twice, once in 1996 as a teen and again when he lost the title in 1999 at age 20.

"Floyd can say what he wants, but I saw Floyd get almost beat by Oscar and when he fought [Jose Luis] Castillo for the first time," Roach said.

Castillo lost the lightweight title to Mayweather via decision in 2002 in what was the toughest fight of Mayweather's career. Mayweather won more convincingly in the rematch later that year. Castillo was one of Pacquiao's main sparring partners to prepare him for the fight with Cotto, so Roach talked to Castillo about Mayweather.

"I talked to him about Mayweather when we had him in camp with us and he told me Pacquiao is faster and hits way harder than Mayweather," Roach said. "I thought Castillo won their first fight. He put pressure on Mayweather and broke him down. Whatever Floyd gives us, we'll take. Manny will him on the arms, the shoulders, wherever he can, and Mayweather will feel it. There's no way Mayweather can win the fight running, and that's what he does best."

If the fight happens, the date of March 13 has been floated. However, Roach thinks that is too soon.

Although Pacquiao beat Cotto, it was a physically demanding fight. Pacquiao suffered a broken right ear drum in addition to the cuts and bruises on his face, Roach said.

"May or June, in that ballpark," Roach said about when he thought the fight should happen. "March may be too close to get a big fight like that going. I'd like to see Manny take a rest and then get into it. We'll have a change in sparring partners and style because Mayweather is so different than our last four opponents [Cotto, Ricky Hatton, De La Hoya and David Diaz]. We have to study him really hard. But I know Mayweather really well. I just need Manny to see what I see.

"I would love to see Manny knock this guy out and then retire," he said. "There's no place to go after that. We will break Mayweather down. He's a fragile guy. I know he is hard to get to but we will get to him. Manny can match Mayweather's speed and he has better footwork and more balls."

While the fight may not ever happen, casinos in Las Vegas are already taking bets on who will win if Pacquiao and Mayweather get into the ring.

Pacquiao opened as an 8-5 favorite at sports books operated by Station Casinos, and it didn't take long for bettors to take a side.

Several $20,000 bets were put down on Mayweather, forcing the line down to 7-5 in the early going, said Art Manteris, the casino operator's vice president of sports book operations.

Dan Rafael is ESPN.com's boxing writer. Information from The Associated Press contributed to this report.