LAS VEGAS — A knockout victory by Conor McGregor against Floyd Mayweather in one of the first four rounds Saturday night could spell disaster for Nevada’s sports books and could precipitate the biggest loss on a sports bet in MGM Resorts’ history.

McGregor has been the fan favorite at nearly every public appearance he has made with Mayweather, as they’ve traveled the world promoting their boxing match Saturday at the T-Mobile Arena.

But there is one group of people who will be rooting mightily for the 49-0 Mayweather: the directors at sports books throughout the state, who have written an overwhelming number of tickets on McGregor to win this unique fight.

At the MGM Resorts properties (which include the MGM Grand, Mandalay Bay, Luxor, Excalibur, Bellagio, Mirage, Monte Carlo and New York New York), there have been 6,500 tickets written on McGregor to win to only 300 for Mayweather.

But the total amount of money wagered there is 60 percent on Mayweather, 40 on McGregor, race and sports book director Jay Rood told Yahoo Sports on Wednesday.

At the Westgate Las Vegas SuperBook, betting action has been nonstop since it first put up a line on the fight in February. Jeff Sherman, the assistant race and sports book manager, told Yahoo Sports that 92 percent of the tickets have been on McGregor.

The smaller sports book at the South Point on the extreme south end of Las Vegas Boulevard has also been deluged by fans looking to wager on McGregor.

“We’re just a tiny little book way out here and given what is going on here, I can only imagine what is going on at those big giant books down on the Strip,” said Jimmy Vaccaro, one of the long-time leading race and sports book directors who is now in charge of the operation at the South Point. “I just called down to see what we were doing. From 8 o’clock last night until just a few minutes ago [around 9:30 a.m. Pacific time on Wednesday], we took $10,000 on McGregor at plus-390 and we had $52,000 on Mayweather at minus-490. This is insane.”

That is the word from sports book directors all over Las Vegas. Vaccaro was the first sports book director at The Mirage when it opened in 1989 and he became famous as the only book to take bets on the Mike Tyson-Buster Douglas heavyweight title fight in 1990.

Tyson was expected to win so easily, no other books put it up. But Vaccaro is a gambler and he was willing to take the action.

“There are things that happen to a person in their lifetime that they always remember, and for me, Tyson-Douglas is one of those,” Vaccaro said. “Some things fade into the background over time, but not that. We opened Tyson at 27-1 and in the next day or so, I got a $54,000 bet on Tyson to win $2,000. [The bettor] was thinking it was going to be like every other Tyson fight and would be a pick-up. Three days later, I was at 32-1 and this guy laid $96,000 to win $3,000. This kept going on for three weeks prior to the fight.

“At 37-1, I can’t tell you how many plays I got at $37,000 to win $1,000. We got up to 42-1 and finally took some money on the dog at that price.

“But the bettors are insistent on wagering on McGregor and aren’t worried about the odds. They’ll stand in line and if the odds drop, they’ll bet him anyway. It’s as if they want to have a ticket and a rooting interest in him, regardless of the price. The smart move would be to wait to see if it edges back up but that’s not happening.”

Rood said major boxing matches normally do 20 times more betting action than similarly major UFC cards. But he said he began to get money on McGregor two months ago and it hasn’t slowed down.

Most of the bets normally come on fight day.

“It’s been fairly hectic,” Rood said. “Not only are we writing a pretty good handle to it, we’re writing an enormous amount of tickets, especially on McGregor. That’s been occurring for basically two months now, which is really odd to write that many tickets that far out from the fight. Traditionally, we take about 90 percent of the money in the last 36 hours.”

The sports books will need Mayweather to win, and preferably by decision. Many fans are also picking McGregor to win by knockout in one of the first four rounds. Rood said action on that bet increased significantly when the Nevada Athletic Commission allowed the boxers to compete in 8-ounce gloves instead of the 10-ounce gloves the rules call for.

Rood said a McGregor win in any of the first four rounds would be “very detrimental to us.”

“The worst-case scenario for us would be if McGregor were to get a TKO or somehow knock him out in the first four rounds,” Rood said. “That would be disastrous for us. It would probably rank as the biggest loss in our company’s history from a race and sports perspective.”

Vaccaro said he felt the true odds of the fight should be 50-1 favoring Mayweather. He said he’s not sure where the line will go because “I’ve never seen anything like this previously. We’re in completely uncharted waters.”

The unique nature of the fight – McGregor is making his pro debut against Mayweather, regarded widely as one of the elite fighters in boxing history – is making Vaccaro take a different stance in booking the bout.

His opinion is baked into the line much more than normal.

“Very, very seldom do you do this as a bookmaker, that you go with the side that you like,” he said. “I’d say 99 percent of the time, you let the money dictate who you’re rooting for. But in this spot, we’re going to go in needing Mayweather, because it’s too good of a spot and we’ll go in and pick up some money.”

Though the money is larger on Mayweather, the liability is greater on McGregor because of the odds. A $100,000 bet on Mayweather might pay out $20,000, but at 10-1, 8-1 and 6-1, those smaller bets on McGregor will eventually overwhelm the Mayweather money, Sherman pointed out.

Across Nevada, bets are rolling in on the fight and it will be the most heavily bet fight in the state’s history by the time the first bell rings.

“It started early and it’s just never stopped,” Sherman said.