Andre Berto has vowed to upset the odds against Floyd Mayweather in the pound-for-pound king’s final fight in Las Vegas on September 12.

Mayweather will put his WBA and WBC welterweight titles on the line when he aims to equal Rocky Marciano's legendary record by retiring with an unblemished 49-0 professional record.

The boxing superstar, who is a prohibitive 1/100 odds-on favorite, is already looking forward to hanging up his gloves with his perfect record intact but Berto has other plans.

"This is going to be for everyone who believes in the underdog," promised 16/1 outsider Berto, who has won 30 fights, but has also lost three times in the last four years.

"From an energy aspect I feel great. It's my first time in a while coming into a fight with no injuries. This is the healthiest I've been since I can remember.

"We're here. It's my time to see him. He can have his 'MayVinci' code because we put in the work. The whole team is confident. I'm going to do what I do.

"We worked on a lot of different things at camp. I have the speed to keep up with him. I have more power. The thing with Floyd is, most guys he fights aren't as athletic as he is. But I am.

"If you come at Floyd fast but don't have a plan and don't have good footwork, it's too easy for him. If you have a guy that's as athletic as him, it gives him problems. There is a lot more to me than just walking guys down. I have speed, I have power, I have a crazy uppercut, I can move to the side. There are a lot of ways I can get it done.

"I'm not going to watch his sparring. I don't want to watch him driving his cars, none of that. I want to see him September 12. This is my first time going into a fight without all the pressure on my back. I've always been the favourite in every fight. I don't know what he's feeling and I don't really have to care about it.

"It's a different mind-set. Coming from where I come from, we always had to defeat the odds. We didn't have what other people had. We had to work twice as hard for everything. To be noticed to be seen. Even back then it drove me to be the best that I can be. I wanted everyone to know I was somebody you had to watch.

"I've faced these odds my whole life. I was discounted two years ago when I was laying in the hospital. I'm constantly envisioning victory. All the hard work we're putting in, it'll all pay off fight night. It's not just for me. I've been through doing things for me. I see what's real now. I've prepared myself mentally to be in this position. People can say whatever they want. We're focused. This is going to be for everyone who believes in the underdog."