Boxing may no longer be the mainstream sports powerhouse it once was, but Floyd Mayweather is proving it's still very lucrative when you're the best in the world. The undefeated American boxer ranks atop ESPN's annual list of highest-paid athletes.   

SportsCenter announced the release of this year's top 25, which is based purely on guaranteed salaries and prize money. For boxers who made the cut, the totals are based on the guaranteed minimum for their 2014 fights. Endorsement deals are not included for any athletes.

Here's the complete list from ESPN:

Headlining these types of lists is nothing new for Mayweather. He's the most in-demand boxer in the world. Therefore, every time he fights, the guaranteed money is off the charts.

In turn, he made over $20 million more than any other athlete during the ranking period. That's nothing short of amazing given the constantly raising salaries around the globe for virtually every sport.

Mayweather spoke about money with Jon Wertheim of Sports Illustrated after ranking first in the magazine's annual Fortunate 50 last year. He said the guaranteed money only scratches the surface of what he could make on a fight night:

It's just more like to say, OK, I'm guaranteed over $30 something million. That's a guarantee, but we ain't talking about how much money I could potentially make. I could go out there and potentially make $60 million a night.

It's the type of payday most people cannot even get their head around. But Mayweather has fought his way up the ranks without losing a single fight (45-0 with 26 KOs), earning the success that's now allowing him to make huge amounts of cash every time he steps in the ring, which is only once or twice per year. Last year, Mayweather fought just twice beating Saul 'Canelo' Alvarez and Robert Guerrero.

Among the other interesting notes to emerge from ESPN's breakdown is the lack of an NHL player in the top 25. In fact, Shea Weber of the Nashville Predators leads the league at $14 million, $9 million short of making the list.

Less surprising is the fact the NFL salaries are dominated by quarterbacks. When you wonder why they get the most attention on a weekly basis, it's because six of the top seven players in terms of salary are those under center. Superstar wide receiver Calvin Johnson is the only exception.

Aside from that, perhaps the only unexpected names on the list from an American perspective are Formula One drivers Fernando Alonso and Lewis Hamilton, who tied for 12th at $27.5 million. That's simply because it's not covered with the same intensity in the United States as elsewhere around the globe.

Regardless of the sport, every athlete has a long way to go before they can catch Mayweather's eye-popping guaranteed income.

With "Money" still fighting and possessing a pristine undefeated record, he will only continue to draw big paydays. His next one will come May 3 when he faces Marcos Maidana at the MGM Grand in Las Vegas. There's no doubt Mayweather will keep raking in the cash and making headlines with each future bout.