But it's Osaka, also the 2019 Australian Open champion, who has soared to the top after benefiting from major appeal in two financial powerhouses.
She was born in and represents Japan, but also has a major US presence after moving to the States as a three-year-old.
"To those outside the tennis world, Osaka is a relatively fresh face with a great backstory," University of Southern California sports business professor David Carter told Forbes.
"Combine that with being youthful and bicultural - two attributes that help her resonate with younger, global audiences - and the result is the emergence of a global sports marketing icon."
A large slice of Osaka's income stems from an apparel deal with Nike that paid her more than $16.1 million in the past year and runs through 2025. Nissan and racquet-maker Yonex are other major backers.
But Osaka also became a hot commodity ahead of the postponed Tokyo Olympics, with sponsors like Procter & Gmable, All Nippon Airways and Nissin jumping on board.
Tennis players have been female sport's top earner since Forbes began tracking income in 1990, with Williams topping the list for the past four years and Sharapova the five before that.
But they still have a way to go to catch the men.
Osaka ranks just 29th on the 2020 Forbes list of the world's 100 top-paid athletes, four spots ahead of Williams, which is due to be released next week.
It's the first time two women have cracked the top 100 since 2016.
