The "World's Highest-Paid Athletes 2018" list is topped by 41-year-old Mayweather, with United States dollars 285 million earnings.
Mayweather earnt $275m (£205.9m) from his fight against UFC star Conor McGregor last August and supplemented his annual income with $10m (£7.49m) in endorsements, Forbes reports.
Lionel Messi was named the second highest earner with pay of $111m (£83.1m) a year ago, with his great rival Cristiano Ronaldo earning slightly less in 2018 with $108m (£80.9m).
Mayweather ranked just 14th in ESPN's third annual World Fame 100 - a ranking that takes into account Forbes' annual list as well as several other metrics. NBA stars lead the way with 40 basketball players among the top 100.
This year 40 National Basketball Association players made the cut in Forbes' annual look at the world's 100 highest-paid athletes, breaking the record of 32 set last year by hoopsters.
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Tennis star Serena Williams, who previous year was the only woman to feature on the list at 51st place with earnings of $27 million, dropped out of the rankings after taking a break from the sport due to the birth of her daughter. Since the list was expanded to at least 50 people in 2010, there had been one woman on the list every single year.
Forbes used salary and bonus data between June 1, 2017 and June 1, 2018 to create the list.
Messi's annual salary and bonus exceeded Dollars 80 million, making him the highest-paid player on the pitch this year.
Second-placed Messi made $111m (£83.1m) thanks to his $84m (£62.9m) in salary and winnings and endorsements worth $27m (£20.2m). Completing the top 10 were basketball's LeBron James (85.5), tennis's Roger Federer (77.2), basketball's Stephen Curry (76.9) and quarterbacks Matt Ryan (67.3) and Matthew Stafford (59.5).
The top 100 has an worldwide flavour with athletes from 22 countries, but Americans dominate the action with 66 making the cut thanks to sky-high salaries in baseball, basketball and football.