Jung Jinsun of South Korea won the bronze, beating Seth Kelsey of the U.S. 12-11 in overtime.
Limardo was seeded 12th and is the highest-seeded competitor to reach the medal round after a series of early upsets. When he scored the final point against Piasecki, he tore off his headpiece, thrust both arms into the air and ran around the arena.
Piasecki had placed 43rd, 65th and 26th, respectively, at the last three world championships. Limardo was seventh at worlds in 2011, and had not been in the top 20 in either of the previous two years.