5★STAR Grand Prix 2021 ~Opening Round: Day 1~ was a professional wrestling event promoted by World Wonder Ring Stardom, held on July 31, 2021 at the Yokohama Budokan in Yokohama, Kanagawa, Japan. It served as the first show for the company's annual round-robin singles tournament and included seven matches from the field of 20 competitors, main evented by reigning World of Stardom champion Utami Hayashishita taking on Maika as part of the Blue Stars block.