Suwon will face Ulsan Hyundai Horang-I in the semi-finals while Incheon United, who defeated Chunnam Dragons, will meet FC Seoul.

AFC Champions League quarter-finalists Seongnam, who top the K-League by six points above second-placed Suwon, took the lead just before the break as defender Cho Byung-kuk slid the ball home from close range.

Suwon pressed for an equaliser and were rewarded with 18 minutes remaining as Ahn Jung-hwan volleyed home from Nadson's header to send the game into extra time.

Baek Ji-hoon put Suwon ahead in the first minute of extra time as the midfielder fired home from outside of the area before Yang Sang-min found Nadson inside the area to double the lead from close range just before the break.

Nadson sealed the win a minute after the restart with a stunning curling long range strike.

In Incheon, Kim Sang-rok put United ahead 10 minutes before the break, but eight minutes later Leandro equalised for Chunnam.

Bang Sung-hwan won the game for Incheon with 18 minutes remaining to set-up a clash with Seoul on June 20.