Tyson Fury launched a tirade of abuse towards Oleksandr Usyk and pushed his head into the Ukrainian at their face-off before the two were separated by security in London.
Briton Fury, 35, takes on Ukraine's Usyk in Riyadh on 17 February - the winner will be crowned the first undisputed heavyweight champion in the four-belt era.
Usyk, 36, is the WBA, WBO and IBF champion with Fury holding the WBC belt.
"You are all dossers. He's going to get knocked out. And you two are going to work for me slinging my bags," Fury told Usyk and his promoter, Alexander Krassyuk and manager, Egis Klimas.
"Sausage, ugly little man, rabbit," Fury continued at Thursday's news conference, aiming more expletives at his fellow champion.
A composed Usyk remained undeterred and reluctant to engage in a war of words.
"Enough? My friend. Have you stopped? Enough? Have you stopped talking?," he asked.
Morecambe's Fury boasts an undefeated record of 34 wins and one draw but is coming off October's unexpectedly close fight against Francis Ngannou.
French-Cameroonian Ngannou, a former UFC champion, was making his boxing debut. Fury edged a split-decision points victory in the non-title bout, although many ringside observers felt Ngannou should have been awarded a shock victory
But any suggestion the below-par Ngannou performance would humble the champion were quashed when the a dancing Fury strutted to the stage on Thursday evening with a swagger.
It took Fury mere minutes to lay into Usyk, interrupting Krassyuk's opening statement.
"You're getting smashed to pieces. Sausage. You're fighting the best British heavyweight there's ever been," he shouted, adding a number of expletives.
"I come here to pick a fight. I didn't come here to play games. I didn't get all dressed up for nothing. I come here to fight. You ugly little man."
Ever unpredictable, Fury then began to compliment the undefeated Usyk's boxing skills and achievements, but the praise was short lived.
Usyk - who has won all 21 pro bouts - defended his titles against Londoner Daniel Dubois in August. He was dropped in the fight by a punch which the referee declared a low blow.
"I think he got hit in the body and he didn't want to get up for five minutes," Fury said. "Crying to the referee. That's what he did."
Usyk replied: "I absolutely don't care what Tyson thinks of that."
As the news conference drew to a close, music from the Rocky movie played as the two men came head to head.
Actor Sylvester Stallone made a surprise appearance and was sandwiched between the heavyweights.
Fury looked to provoke his opponent by forcefully driving his head into Usyk, who held his ground before security intervened, with Stallone swiftly departing.
After Tuesday's announcement that a blockbuster card featuring Deontay Wilder and Anthony Joshua will take place in Riyadh on 23 December, arguably the biggest fight in world boxing is also heading to the Saudi capital.
It will form part of 'Riyadh Season' - an entertainment events festival held in Saudi Arabia's capital every winter since its launch in 2019.
The Gulf Kingdom has become the global hub for boxing but has provoked scrutiny due to the country's poor human rights record - 81 men were executed on one day last year - women's rights abuses, the criminalisation of homosexuality, the restriction of free speech and the war in Yemen.
Analysis - 'Fury brought heat, Usyk the coolness'
The vibrant Outernet in central London is the same venue where a Fury-Ngannou news conference was held in September. On that night, a jovial Fury was as brash as ever.
On Thursday, he turned it up a notch. Fury's first words on the microphone were to thank the public for voting him the world's sexiest sportsman in a recent poll.
The tagline for the biggest heavyweight fight in recent memory reads 'Ring of fire' - Fury brought the heat, Usyk the coolness. There has not been an undisputed heavyweight champion since 1999 when Lennox Lewis beat Evander Holyfield to defend the WBA, WBC and IBF titles.
While there is no clarification on any rematch clause for either fighter, Fury's promoter Frank Warren said there could be a second fight depending on the outcome of the first.
"If it's a great fight I'm sure everyone will want to see it," Warren told BBC Sport.
Team Fury also intends to face Ngannou again. The boxing novice entered the WBC rankings at number 10 this week - any rematch could potentially be for Fury's world title.
Fury has incessantly taunted Usyk in social media posts over the past year or so, repeatedly labelling him a "dosser". Usyk sometimes gives as good as he gets, but here he took a back seat.
There is a mutual respect but Fury's antics at the head-to-head aggrieved Usyk's team. A fight of this magnitude perhaps does not need any pantomime, but Fury will forever be the showman.