5★STAR Grand Prix 2021 ~Opening Round: Day 2~ was a professional wrestling event promoted by World Wonder Ring Stardom, held on August 1, 2021 at the Yokohama Budokan in Yokohama, Kanagawa, Japan. It served as the second show for the company's annual round-robin singles tournament and included seven matches from the field of 20 competitors, main evented by faction leaders Mayu Iwatani (STARS) and Giulia (Donna del Mondo) facing off as part of the Red Stars block.