203rd-ranked Karsten Braasch lost in the 1st round of the 1998 Australian Open. He then beat Serena and Venus Williams back-to-back easily, 6-1 and 6-2. Cute story really, unless you refuse to recognize there are physical differences between men and women.
https://www.tennisnow.com/Blogs/NET-POSTS/November-2017-(1)/The-Man-Who-Beat-Venus-and-Serena-Back-to-Back.aspx
