Floyd Mayweather said "the world will stop" when he fights Manny Pacquiao on 2 May as they were face-to-face for the last time before the weigh-in.
Mayweather, who has won all 47 of his fights, told Pacquiao at a press conference in Los Angeles on Wednesday that he was not ready to taste defeat.
Pacquiao had earlier said that he would beat the American for the good of boxing.
The Filipino fighter has a record of 57 wins, two draws and five losses.
"May 2 - the world stops. Mayweather v Pacquiao is the biggest fight in history," Mayweather said.
The fight, which has been the subject of on-off contract negotiations over six years, is expected to generate as much as £162m ($250m).
Who won the verbals?
In low-key speeches in front of about 700 media, both fighters spent more time talking up the fight than aiming barbs at their opponent.
Mayweather, 38, suggested that his unblemished record may give him a psychological advantage over Pacquiao, claiming that "if you lose, it is always in your mind", but also praised the Filipino's camp for making the fight happen.
"I have to be thankful that we have all come together as one to give the world what they want to see," he added.
Pacquiao, who made several references to his Christian faith in an unremarkable address at the news conference, had tweeted criticism of Mayweather's lavish lifestyle earlier in the day.
"Beating Floyd is good for boxing. When athletes have great success, their success goes to their head. That is bad for boxing," he wrote.
"I'm here to prove that I can easily beat the undefeated."
The fight is expected to boil down to whether Pacquiao's speed and power can ruffle Mayweather's supreme defensive skills. Pacquiao was in no doubt he could win, referencing his victories over heavier-hitting fighters than Mayweather.
"My footwork and hand combinations will be my advantage. I tell you Miguel Cotto and Antonio Margarito punch hard. This is boxing and its about punches," he added on Twitter.
"We're gonna kick his ass!"
It was left to Pacquiao's trainer Freddie Roach to deliver the usual pre-fight bombast.
"We're fighting the best fighter in the world - but we're gonna kick his ass," he told the media, drawing smiles from Mayweather.
Earlier, on the red carpet at a Nokia Theatre venue that is more used to hosting the Emmy television awards, he told BBC Sport why he was confident Pacquiao, 36, could inflict Mayweather's first defeat.
"My guy is too fast, he hits too hard. I think Floyd's legs are shot," he said.
He says he wants to stand and trade more and entertain the fans more, but I don't think that is true. He has to say that."
Hottest ticket in town
The cost of seeing the fight in the person was revealed with ticket prices to range from £1,004 ($1,500) to £5,023 ($7,500).
However, it is widely expected that tickets will never actually go on general sale, with celebrities and connections expected to fill the MGM Grand to capacity.
It has been reported that even the well-connected may need to guarantee a certain spend at the venue's casinos to ensure a ringside seat.
Justin Bieber seems likely to be in attendance. The Canadian pop star, a friend of Mayweather's, made a cameo appearance as the fighters posed of more publicity shots.