International defender Kwak Tae-hwi fired home the decisive penalty as Seoul, who finished third in regular competition, missed three spot kicks as their season came to an abrupt end.

Chunnam, who ended the regular season in sixth, advance to the next round where they will face the winner of tomorrow's meeting between Seongnam Ilhwa Chunma and Incheon United.

If Chunnam prevail they will face Asian Champions League winner Pohang Steelers in the semi-final with Jeonbuk Motors awaiting the winner in the final.

Chunnam took the lead after 12 minutes as Adrian Chuva's cross-field pass found Lee Gyu-ro in space and the striker chested the ball down in the area before unleashing a fine half-volley past Kim Ho-jun.

But Seoul were level three minutes later as Ki Sung-yong's perfectly weighted defence-splitting pass gave Jung Jo-gook a simple tap-in from close range for the home side.

Despite the fast start, from then on chances were at a premium and the game drifted into extra-time.

The closest either team came to adding to the scoreline was with two minutes remaining in extra-time when Ki drew a sharp save from Chunnam goalkeeper Yeom Dong-gyun.

In the shootout, Ki Sung-yung, Lee Sang-hyub and Lee Jong-min all failed to convert for Seoul before Kwak fired home in emphatic style after FC Seoul goalkeeper Kim had saved two spot kicks.