Tennis superstar Naomi Osaka set a record for most money earned by a female athlete in a 12-month period.
Badenhausen noted Williams held the title of highest-paid female athlete for each of the past four years; the previous high-water mark for a female athlete in a single year was the $29.7 million Maria Sharapova made in 2015.
Osaka, 22, had her breakout moment at the 2018 U.S. Open when she defeated Williams in the final. That victory made her the first Japanese-born player to win a Grand Slam event.
The 2019 Australian Open was another crucial point in Osaka's career. Winning a second straight Grand Slam title, with a three-set victory over Petra Kvitova, moved her up to No. 1 in the world rankings for the first time.
A Florida resident, Osaka won a career-high three tournaments in the 2019 season and made $6,788,282 in prize money, per ESPN.com. She's 10th in the WTA Tour rankings this year, one spot behind Williams.
Badenhausen estimated that Osaka made $16 million in endorsements for the 12-month period from June 1, 2018, to June 1, 2019, thanks to deals with Mastercard, All Nippon Airways, Nissan and Procter & Gamble.
A dual citizen of Japan and the United States, Osaka previously announced she will represent Japan during the Tokyo Olympics that have been delayed until the summer of 2021 because of the coronavirus pandemic.
Per Badenhausen, Osaka became "an even hotter commodity" in the eyes of Olympic sponsors when she chose to take part in the Games as a representative of Japan.
Even though the full list of Forbes' 100 highest-paid athletes won't be available until next week, Badenhausen noted Osaka will rank No. 29 and Williams will be No. 33.