Floyd Mayweather and Conor McGregor lit the touchpaper for their cross-combat superfight here Tuesday, turning the air blue in an expletive-laden face-to-face meeting to launch their global promotional tour for the bout.

More than 11,000 fans crowded into Los Angeles's Staples Center for a raucous first live showdown between former boxing world champion Mayweather and Irishman McGregor, one of the biggest stars of mixed martial arts.

The two men are set to face each other in Las Vegas on August 26 in what could be the richest fight in history after finally agreeing to climb into a boxing ring following a year-long guessing game over whether they would ever do battle.

Tuesday's fiery face-off saw the swaggering, cocksure McGregor strut onto stage confidently in a three-piece suit featuring pinstripes made up of an offensive two-word insult.

The immaculately tailored profanity set the tone for a spectacle shot through with an endless torrent of abuse from both fighters, no doubt delighting promoters as they drum up hype for a bout which will demand $10,000 for ringside seats.

The suited McGregor was the first to take the microphone, mocking Mayweather's decision to show up wearing a Stars and Stripes tracksuit, suggesting it was linked to the American's reported tax difficulties.

"He's in a tracksuit, he can't even afford a suit anymore!" McGregor declared to roars of laughter from the massed ranks of his green-shirted fans crammed into the lower tiers of the famous basketball arena.

McGregor, who will start as an overwhelming underdog against one of the most accomplished defensive fighters in history, was bullish about his prospects of victory. "The 0 has got to go," McGregor declared, referring to Mayweather's perfect 49-0 record.

"I'm going to knock him out inside four rounds, mark my words," McGregor said, to more roars. "On August 26, this man will be unconscious, he's too small, he's too frail."

"I will come out and paint many pictures. I can fight in my styles. I can dazzle him."

A stony-faced Mayweather meanwhile bided his time before taking the microphone and uncorking his own cascade of expletives.

"I'm going to knock this bitch out," Mayweather said, to boos from the crowd. McGregor shot back: "You haven't knocked anyone out for 20 years!"

Mayweather meanwhile responded to the jibes about his finances -- he recently filed for an extension to pay his 2015 tax bill -- by producing an uncashed check for $100 million from an assistant's rucksack.

McGregor was again ready with a riposte: "Give it to the taxman!"

Mayweather, 40, was unruffled, vowing to administer a comprehensive victory over the 28-year-old Irishman despite giving away 12 years to his younger opponent.

"I'm not the same fighter I was 10 years ago. Or 5 years ago. Or 2 years ago," Mayweather said. 

"But I've got enough to beat you. He can choose which way he wants to go. Either on his back or on his face."

- Snarling braggadocio -

Mayweather later appeared relaxed during a briefing with print reporters, suggesting his snarling braggadocio on stage had been solely for the benefit of the fans who had flocked to the arena.

"We have to give people what they want to see," the former welterweight king said. 

"That's what the people wanted to see. To have a sold-out arena like today and give these fans something real smooth and calm? They don't want that. That's not what they wanted. These fans want entertainment. They got entertained today by both competitors."

Unsurprisingly Mayweather declared himself the victor in the verbal sparring, saying McGregor's incessant trash-talking indicated he had rattled the Irish fighter.

"He's got to realise, I've been here before," Mayweather said. "He just started this. I've been doing this for years. Years after years. He's upset. He's ready to kill me now. He's mad. I was calm, cool. 

"I gave him a little bit of his own medicine and he didn't like it."

Source: AFP