Last year's AFC Champions League finalists FC Seoul scored in each half to hand the Central Coast Mariners their fifth straight defeat in all competitions.
A dubious penalty awarded against Josh Rose and scored by Spaniard Osmar in the first half set the Korean outfit on their way to extending their impressive home record to 11 matches unbeaten in the ACL, 21-year-old Yun Il-lok sealing the comfortable triumph in the second half.
As if losing the match wasn't bad enough for the A-League side. centre-back Marcel Seip was sent off for a high foot on goal-scorer Yun with six minutes remaining.
Seoul were missing Colombian Mauricio Molina following a reported falling out with coach Choi Yong-Soo. The Mariners returned Nick Fitzgerald, Matt Simon, and Rose to the line-up who all missed the loss to Wellington on Friday last Friday due to suspension. With Eddy Bosnar absent due to a back issue Dutchman Seip replaced him.
Both sides were comfortable to play a possession-based game early in the match on the somewhat bumpy pitch, which had recently been re-laid, in near freezing temperatures in the Korean capital.
Central Coast's chances were limited to hopeful switches of play early on as they struggled to adapt to the conditions.
The visitors survived three near misses in quick succession after 14 minutes when goalkeeper Liam Reddy first saved a strike from defender Osmar, Seip blocked a shot from Sergio Escudero and John Hutchinson, defending on the post, helped to clear Yun's attempt.
After 31 minutes the Mariners fell victim to a woeful decision which resulted in Osmar scoring the decisive goal via the resultant 33-rd minute penalty.
As Spanish-born attacker Escudero was moving away from goal on the edge of the area he was collected late by Mariners defender Rose in a soft challenge but Saudi official Fahad Al Mirdasi, seemingly after prompting from his assistant on the near side, pointed to the spot.
After the controversial decision Osmar snuck the ball in behind Reddy before it cannoned in off the right-hand upright and nestled in the net.
While offering little in attack - the home side had 68 percent of first-half possession - the Mariners were comfortable enough in dealing with the crosses of defender Cha Du Ri, who seemed the main attacking vehicle for the K-League side until the penalty decision.
The 51st minute saw the Mariners' best chance of the match arrive, when Rose blasted a shot over the bar on his non-preferred right foot, Bernie Ibini having provided the cross following some neat Mariners midfield play.
Six minutes later the Koreans doubled their lead when Escudero dummied over a cross from Kim Chi-Woo on the left-hand side, which Yun lashed home.
Kim nearly turned goal-scorer in the 62nd minute after picking up the assist moments earlier when he forced a great save from former Sydney FC shot-stopper Reddy.
After the second goal the Mariners kept their deep-lying game plan but were outnumbered on the odd occasion they were able to open up via a counter-attack and the home side eased to victory.
The Mariners will return to the domestic competition this weekend, facing Sydney FC in Gosford, as they attempt to improve on sixth spot.
Seoul's win means they lead the group after Sanfrecce Hiroshima and Chinese side Beijing Guoan drew 1-1 in Japan in the other fixture.