ONE Fight Night 21: Eersel vs. Nicolas was a combat sport event produced by ONE Championship that took place on April 6, 2024, at Lumpinee Boxing Stadium in Bangkok, Thailand. A ONE Lightweight Kickboxing World Championship bout between current champion (also current ONE Lightweight Muay Thai World Champion) Regian Eersel and Alexis Nicolas headlined the event.

ONE Fight Night 21: Eersel vs. Nicolas (2024) is currently not available on any services.