John Riel Casimero vs. Guillermo Rigondeaux, was a professional boxing match contested on August 14, 2021, for the WBO bantamweight championship.

In April 2021 it was announced that Casimero would defend his Bantamweight title against two-time Olympic gold medalist and 2-division world champion Guillermo Rigondeaux.

[1] On June 19, however he was replaced by WBC champion Nonito Donaire, with Rigondeaux likely to face an opponent undercard.

[4] The bout took place at the Dignity Health Sports Park, Carson, California U.S.[5] In an extremely uneventful bout, Casimero pressured his opponent all night, fighting on the front foot and throwing more punches than Rigondeaux, who was reluctant to engage.

In his post-fight interview, Casimero criticized his opponent's extremely passive gameplan, saying "I'm focused on [the] knockout, but Rigondeaux always runs.