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.

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

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.

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.

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

“He has to realize I have been here before,” Mayweather said. “I’ve been doing this for years. He’s ready to kill me now. I gave him a little bit of his own medicine, I let him do his talking, and then let him have it. And he didn’t like it.”

“He is going to be upset. He is going to go out and try to come out and kill me. My dad (trainer Floyd Mayweather Sr.) is going to have a great game plan. (McGregor) really wants to win bad. Other fighters, it plays out one of two ways when you face (me). Some guys play it safe, some guys go straight for the kill. He is a heavy hitter so I have got to be cautious.”