Naomi Osaka (大坂 なおみ, Ōsaka Naomi, born 16 October 1997) is a Japanese professional tennis player. She is the reigning US Open champion in women's singles. Osaka has a career-high Women's Tennis Association (WTA) ranking of No. 4 in the world, which she achieved in October 2018. She has won two titles and reached four finals on the WTA Tour.
Osaka first came to prominence at the age of sixteen when she defeated former US Open champion Samantha Stosur at the 2014 Bank of the West Classic, which was her first time in the main draw of a WTA tournament. She reached her first WTA final two years later at the 2016 Toray Pan Pacific Open, which took her into the top 50 in the world rankings. Her breakthrough year was 2018; in March she won Indian Wells, beating former world number ones Maria Sharapova and Karolína Plíšková in the first round and quarterfinals respectively, before defeating current No. 1 Simona Halep in the semifinals. In September, she won the 2018 US Open, defeating 23-time Grand Slam champion Serena Williams in the final, and becoming the first Japanese player to win a Grand Slam singles tournament.