The 36-year-old welterweight - considered the best defensive boxer of his generation - topped the magazine's Fortunate 50 list, issued on Wednesday. Mayweather also took the top spot last year, earning an estimated $85 million, again from just two fights, the magazine reported.
Miami Heat basketball star LeBron James, 28, a four-time National Basketball Association Most Valuable Player, came in this year in the number two slot, earning a total of $56.5 million.
The list is calculated by combining estimated salary, winnings and endorsements. Mayweather's total earnings are even more impressive considering he received no endorsement money either this year or last.
James' $56.5 million income combines a $17.5 million salary with an additional $39 million in endorsements.
Golfer Tiger Woods, the highest paid U.S. athlete from 2004, when the list was first published, through 2011, dropped to the No. 5 slot on this year's list, earning $40.8 million.
Chicago Cubs outfielder Alfonso Soriano came in as the 50th highest-paid U.S. athlete with an estimated $18.2 million.
Candidates for the list must be U.S. citizens and compete in a U.S.-based league.
Internationally, soccer great David Beckham is estimated to earn more than $48 million, landing him the top spot on the magazine's annual list of highest-paid athletes worldwide, The International 20.
(Reporting by Chris Francescani; Editing by Cynthia Johnston and Tim Dobbyn)