John Riel Casimero has four losses against four opponents on his boxing record. For a list of Casimero's best fights, refer to "Best fights of John Riel Casimero".
On September 16, 2017 John Riel Casimero faced off against Jonas Sultan in a flyweight bout at age 28. He was coming in with a record of 24-4 (15), and Sultan was 25 years old and with a record of 13-3 (8). Casimero lost the fight via 12-round unanimous decision.
On June 27, 2015 John Riel Casimero fought Amnat Ruenroeng in a flyweight world-title fight for Ruenroeng's IBF title. Casimero was 26 years old and with a record of 21-3 (13), and Ruenroeng was 35 years old and with a record of 15-0 (5). Casimero lost the fight via 12-round unanimous decision.
On March 26, 2011 John Riel Casimero fought Moruti Mthalane in a flyweight world-title fight for Mthalane's IBF title. Casimero was 22 years old and with a record of 14-2 (8), and Mthalane was 28 years old and with a record of 26-2 (17). Casimero lost the fight via 5th-round TKO.
On July 24, 2010 John Riel Casimero met Ramón García Hirales in a light-flyweight (WBO) world-title defense fight. Casimero was 21 years old and with a record of 14-1 (8). Casimero lost the fight via 12-round split decision and lost the title.
