Full results of the other 98 male athletes' earnings are scheduled to be released next week, but this marks the first time since 2016 that two sportswomen have made the top 100. Sharapova held the honor the previous five years, earning at least $24.4 million in each year from 2011 to 2015.
Williams had annual incomes from $18 million to $29 million and has collected almost $300 million, much of it in endorsement deals.
Osaka was a popular endorsement figure in Japan ahead of the now-postponed Tokyo Olympics and figures to remain a sponsorship dream through next year's rescheduled Games.
Sharapova's surprise departure and Williams' mooted retirement may have worked in Osaka's favour after Nike won a bidding war with Adidas to supply her apparel, paying $10 million for the privilege until 2025.
Roger Federer was the highest earner in the sport past year, collecting an astonishing $93.4 million that included enormous backing from the likes of clothing line Uniqlo, with whom he has a $300 million long-term deal.