Conor McGregor claimed he has never seen Floyd Mayweather in worse physical shape as the pair exchanged words at a raucous weigh-in in Las Vegas.
McGregor weighed in at 153lbs for Saturday's 154lb fight, with Mayweather 149.5lbs, before a face-off that drew roars from the thousands in attendance.
McGregor screamed in the face of his rival and paraded around the stage as Mayweather cut a reserved figure.
"He looks blown out, full of water," said McGregor, 29.
"That's the worst shape I've ever seen him in. I am going to breeze through him, trust me."
The build-up to the T-Mobile Arena bout has at times resembled a soap opera but finally, at around 04:00 BST on Sunday morning, they will at last fight.
If we get a bad result, which for us is McGregor knocking Floyd out in the first four rounds, we could lose around $20m, by far the worst boxing result in the state's history
Mayweather, who has come out of retirement for a 50th and final bout, said: "I know what it takes when it's a fight of this magnitude.
"Weight doesn't win fights, fighting wins fights. It won't go the distance, mark my words. This will be Conor McGregor's last fight also."
Some in Las Vegas thought McGregor's more conservative performance at Wednesday's final news conference intimated he might be coming to terms with the realities of making his boxing debut against one of the greatest fighters of his generation.
But playing to a crowd filled with Irish colours and songs, he revelled in his reception - and in the boos for Mayweather - beating his chest and screaming repeatedly.
"Look at me, I am in peak physical condition," he said, adding he would weigh close to 170lbs on fight night.
Many from within boxing have rubbished the match, choosing to refer to it as an "event" rather than a fight. But the dissatisfaction of the boxing purist looks unlikely to affect the mass audience, with the bout being screened in more than 220 countries, according to Showtime executive vice president, Stephen Espinoza.
That global reach could see the record of 4.6 million pay-per-view buys - set when Mayweather beat Manny Pacquiao in 2015 - beaten.
Watching the fight costs a minimum of £20 in the UK but around £75 in the US. This, added to ticket sales, merchandise and sponsorship, makes for a healthy pot. Tickets are also on sale to watch in bars on the Las Vegas strip, while more than 400 cinemas across the US will broadcast the event.
It all means more than $600m (£466m) could be generated, with Pacquiao-Mayweather's reported haul of around $620m in sight. Mayweather is expected to make around $300m, McGregor $100m. Not bad for 36 minutes of work or less.
Revenue from Saturday's fight could break the record of $620m set by Mayweather's bout against Manny Pacquiao in 2015
Mayweather dominance - in stats
There have been reports 'Money Man' has not taken McGregor seriously. This week 5 live boxing analyst Steve Bunce said only a "cocktail of age setting in and underestimation of his opponent" could pose any danger to the favourite.
Mayweather's father, Floyd Sr, this week told media his son had lost "a lot" of his ability since retiring in 2015. But a 50th career win from 50 fights would carry his son past the late Rocky Marciano's perfect 49-fight record, rounding off a dominant professional career that began after he had won bronze at the 1996 Olympics.
Mayweather has boxed 387 professional rounds, McGregor none.
26 of Mayweather's 49 wins were on points but in 23 of those wins he was given the decision unanimously.
Mayweather has suffered one knockdown in his career. He took an eight count against Carlos Hernandez in 2001.
Betting markets have bemused those who give McGregor no hope as his price has shortened in recent weeks. At around 10-3, the boxing debutant is actually a shorter price than many of the fighters Mayweather dealt with before retiring in 2015.
Las Vegas is expecting more than 1,300 private jets to land before for the weekend's action and the high rollers who hit the city's famous strip traditionally bet big on Mayweather in his home city.
"If we continue as we are, we will rival the $50m record staked in the state of Nevada, set when Mayweather beat Pacquiao," said Jay Rood, who runs the sportsbook at the MGM Grand.
"If we get a bad result, which for us is McGregor knocking Floyd out in the first four rounds, we could lose around $20m, by far the worst boxing result in the state's history."
Closer to home, one Irish bookmaker claims an individual has placed £650,000 on McGregor in a bid to win £2.8m. And while we are talking betting, Mayweather has said he will tweet a picture of his betting slip when he wagers on himself.
'I don't think he'll get lucky; Floyd doesn't let you get lucky'
Packie Collins - trainer and brother of former world champion Steve: "I've been around the game for a long time, even based in America with my brother when Marvin Hagler was fighting. I've never seen anyone train or practise as hard as Conor McGregor. I give him a chance in there."
Chris Eubank - former two-weight world champion: "Everyone is underestimating the Irish spirit. They have ghost-like spirit in warfare. I've felt it. I'm still wondering now how I got beat by Steve Collins in 1995. If McGregor pulls it off it is arguably the greatest upset in history. Everything can happen, that's why I've travelled. It is not a farce."
Jeff Mayweather - uncle of Floyd: "Everyone knows what this fight is about. It's about money. Conor McGregor boxed at one point in his life but didn't master it. Floyd is a master at it."
Rickie Hatton - beaten by Mayweather in 2007: "I don't really give McGregor any chance and I hope I'm wrong. But the only way he could possibly win would be if Floyd Mayweather gets careless or takes a few risks or anything like that - but Floyd never does that, does he? I don't think he'll get lucky; Floyd doesn't let you get lucky."
Amir Khan - former light-welterweight world champion: "It's not only a fight for McGregor and Mayweather, it's a fight between MMA and boxing. At the moment UFC is hitting huge pay-per-view numbers in the US. It's critical for boxing Mayweather wins. I think it could turn some UFC fans back to boxing."
Hall of fame referee Joe Cortez, who has helped McGregor adjust to boxing rules - "He is one of the best learners I have seen. He picked up everything so quick. I've found him to be a gentleman behind the scenes. He's a class act with his girlfriend and baby - a gentleman."
The Mayweather-McGregor fight could get a Hollywood makeover after Saturday night
Fight has met film regularly when it comes to boxing, and a McGregor win might well one day inspire a Hollywood reimagining of Saturday's action.
The contrasting environments in which each man has trained hark back to Rocky IV, where Rocky trains in the Siberian mountains, chopping wood and resorting to old-school training methods, while Ivan Drago works out in a state-of-the art facility.
Mayweather is the traditionalist of this pair, working out from his renowned yet simple Mayweather Boxing Gym. McGregor on the other hand has had access to every gizmo under the sun at the UFC's new Performance Institute - altitude chambers, underwater treadmills, you name it.
He's the Drago figure in this scenario - and things did not work out too well for the Russian.