After the various conferences that took place in July over their world tour, the one on Wednesday (23 August) was more subdued and professional, with both fighters seeming to have been worn out from a month's work of promotion.
However, McGregor was still confident in his prediction that he would finish "Money" off quickly, warning him that he should have just left him be in the sport of mixed martial arts.
"I'm gonna f**k this boy up, make no mistake," McGregor said, as quoted on MMAFighting. "And when it's all said and done, you know what? I'm going to feel a little bit sad, because you should have all left your mouth shut."
"You should have left me over in that game where I'm from, that more ruthless game where we bounce heads off the canvas and drill them through the floor. You should have left me where I was."
With the fight now being contested with eight-ounce gloves — previously 10-ounce — the Irishman added that Mayweather made a big mistake by proposing the change in glove size.
"Eight-ounce gloves, he made a big, big error in my opinion," he added. "I don't see him lasting two rounds. I feel I have the decision to end it inside one."
"He messed up with those eight-ounce gloves. It was amusing and all that, but I'm very, very happy for eight. We usually fight in four, we're going to fight in eight. Keep your hands up, keep your hands down, I don't care. I'm going to break through whatever is in front of me."
The UFC lightweight champion also spoke of how he may create his own hybrid sport, combining the boxing ring and the octagon, once he rules both sports.
When it was Mayweather's turn on stage, he interestingly received a better reaction for a change as the former five-weight champion reiterated that he was taking this fight seriously.
"To be in a combat sport, no matter if it is MMA or boxing, we're fighters at the end of the day," Mayweather explained. "To be in a sport 21 years, I had to take it extremely serious."
"And for you guys to think that Saturday, I'm not taking this serious, I'm taking this extremely serious. But the thing is this, when all is said and done, I know one thing that I can do: I can fight. I can give it and I can take it. But for me to be 49-0 it's obvious I'm not receiving, I'm giving."
Mayweather added that the likes of Saul "Canelo" Alvarez, Manny Pacquiao and Shane Mosley also had bombs in their hands but were unable to do anything to him, implying that McGregor's punching power would have no effect on him.
The duo then took media questions before having a final face-off with the "Money Belt" being paraded behind them that the winner on Saturday will receive.
You can watch the full press conference below.