Ever since Forbes began composing the list, there has always been at least one female athlete included - with as many as three doing so at the peak.
Even so, Forbes reported that Williams earned an estimated $18 million a year ago because of deals with the likes of Nike, JPMorgan Chase, Gatorade and others.
Floyd Mayweather is the champ at making money. He is shown to have a salary/winning of $4m and endorsements worth $20m.
The Forbes list factored in prize cash, salaries and bonuses earned between June 1, 2017 and this past June 1.More news: Covington Wins Interim Title With Decision Over RDA
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His rival Ronaldo, who was top of the list the two previous years, drops to third with $108m (£80.9). "But basketball players dominate the top 100 overall thanks to a soaring salary cap triggered by the NBA's $24 billion TV contract".
Mayweather now has been the highest-paid athlete four times in the last seven years.
Irish mixed martial artist McGregor ($US99 million; $130 million) and Paris St Germain's Neymar ($US90 million; $118 million) were fourth and fifth, respectively, but for the first time since 2010 there was not a single woman on the list. Argentine footballer Lionel Messi, who also plays for Barcelona is ranked second in the list, followed by Real Madrid's Cristiano Ronaldo.
Kurt Badenhausen, Forbes' senior editor, told CNN Sport that on endorsements alone Williams would be ranked in the top 10. Cristiano Ronaldo (Portugal) Soccer $108 million 4.
Between them, the top 100 earned a collective $3.8bn during the past 12 months, which represents an increase of 23% from 2017.
The top is dominated by American sportsmen including LeBron James and two National Football League quarterbacks, but there is no room for New England Patriots' hero Tom Brady.