Ultimate Fighting Championship: Moment of truth in Floyd Mayweather vs Conor McGregor

Floyd Mayweather and Conor McGregor prepared for their money-spinning showdown on Saturday as Las Vegas crackled with anticipation for what is poised to become the richest fight in history.

Undefeated welterweight boxing world champion Mayweather and mixed martial arts star McGregor were expected to touch gloves at around 9:00 pm (0400 GMT Sunday) before 20,000 fans at the T-Mobile Arena.

The controversial 12-round showdown between two of the biggest names in their respective disciplines has captured the imagination of combat sports fans while drawing near universal derision by many in boxing as a farcical mismatch.

Mayweather, who retired unbeaten in 2015 with a perfect 49-0 record, is widely expected to inflict a one-sided defeat on McGregor, a two-time world champion in MMA's Ultimate Fighting Championship who has never boxed professionally.

Veteran trainer Teddy Atlas predicted a rough night inside the ropes for McGregor.

"Would a ping-pong player have a chance of scoring a point against Roger Federer?" Atlas said."It's going to be like walking through a really bad neighbourhood late at night. McGregor's going to get mugged."

In a column for Britain's Daily Mirror, Irish boxing legend Barry McGuigan was even more blunt: "McGregor cannot beat him."

The high-rollers of the gambling world agree, with the lion's share of the money being bet on the fight placed on Mayweather.

As of Saturday, four separate bets of $1 million or more had been placed on Mayweather to win. Those wagers included a $1.2 million cash bet that will earn around $240,000.

William Hill US said the amount of money wagered on the fight had already surpassed any other bout in Las Vegas history.

Yet the fact that so many in the boxing and betting world see the outcome of Saturday's contest as a foregone conclusion has not deterred the massed ranks of McGregor's Irish supporters.

The Las Vegas streets surrounding the fight venue following Friday's weigh-in were transformed into a sea of emerald green as McGregor's raucous army of supporters danced and chanted under blazing sunshine.

While ringside tickets were being offered on secondary markets this week for as much as 102,000 each, some seats inside the T-Mobile Arena were still for sale on Saturday.

Many fans will take the cheaper option of watching the fight at closed-circuit screenings at casinos throughout Sin City.

Parking for private jets at Las Vegas's McCarran International Airport meanwhile was expected to reach capacity as a deluge of celebrities began arriving for the fight.Stacked odds:

The stacked odds against McGregor are also unlikely to put off casual sports fans, with millions of viewers across the United States expected to pay $99.95 to watch on pay-per-view television.

Stephen Espinoza, the head of cable network Showtime Sports which is selling the fight in the US, said surveys had shown that fans were not bothered by predictions of a one-sided bout.

"The casual fans were absolutely adamant," Espinoza said.

"Their response almost universally was 'We don't care if it's a mismatch ... if there's a .01 (percent) chance that something incredible could happen, we need to watch it.'

"And that's why they're going to watch it."

Some projections have indicated the fight is on track to surpass the 4.6 million pay-per-view buys of Mayweather's 2015 "Fight of the Century" against Manny Pacquiao.

If that happens, the bout is almost certain to become the richest fight in history and will leave Mayweather and McGregor laughing all the way to the bank.

ESPN reported on Saturday that Mayweather is guaranteed a $100 million purse from the fight, which could reach $250 million if the most bullish pay-per-view targets are met.

McGregor, a 29-year-old former plumber who was living on unemployment benefits four years ago, is guaranteed $30 million, but could pocket as much as $100 million, ESPN said.

Both Mayweather and McGregor have spent large parts of the build-up to the fight trash-talking, with an ill-tempered global promotional tour laced with expletives, repeated homophobic slurs and allegations of racist language.

McGregor snarled and yelled into Mayweather's face on Friday when the two men went nose-to-nose at their weigh-in.

McGregor taunted Mayweather after tipping the scales at 153 pounds, well inside the 154-pound limit, but substantially heavier than his opponent, who weighed in at 149.5 pounds.

A nonplussed Mayweather shrugged off his weight disadvantage and vowed to stop McGregor inside the distance.

"Weight doesn't win fights, fighting wins fights," Mayweather said. "It won't go the distance. Mark my words -- I'm not worried about the scales."