In 2011, Won entered his first World Championship Final, the 16th Samsung Cup, by defeating Pak Yeong-hun in the quarter-finals, and Chen Yaoye 2-1 in a hard fought semi-final to face the defending champion Gu Li, who respectively defeated former winner Lee Chang-ho, then rising Korean star Na Hyun 2-0.
The first battle scene shifted to the bottom-left hand corner, and Won immediately had to break up White's territorial/positional advantage.
It seemed like a territory endgame was to be handed to Black due to his marginal lead despite the 6.5 komi, but a mistake on move 189 gave Gu an opportunity to strike and drag the game into a closer fight.
This remains to date Won's only World Championship and, despite the victory, he has to perform the compulsory 2-year military service of South Korea.
This is due to the Hanguk Kiwon and the Korean Military's mutual agreement that players who won major international titles outside Korea, i.e. the Fujitsu Cup and the Ing Cup, were able to be exempt from it, whilst domestic titles still required the player to perform military service.