Aidil Sharin made two changes from the side that hammered Hong Kong's Wofoo Tai Po last week with David Rowley and Shahril Sa'ari replacing Zaquan Adha and Ifwat Akmal respectively.
Those changes designed to make Kedah a little more compact in midfield with Rowley's presence tuck alongside Baddrol Bakhtiar and Amin Nazarin with Kpah Sherman asked to feature in a wider berth.
And for a large part of the first half, it was a ploy that worked with Kedah managing to hold Seoul out even though Shahril was constantly kept on his toes with the home side asking the early questions.
The big turnaround in the match came in the 37th minute when centre back Renan Alves collected his second yellow card and conceded a spot kick to Seoul in one fell swoop.
Former Monaco and Arsenal man Park Chu-young easily beat Shahril for the opener with Aidil forced to sacrifice Rowley with Zulkhairi Zulkeply, to shore up the defence.
The Koreans made full use of their numerical advantage to double their lead just four minute into the second half when Park Dong-jin rose highest to thump a header past Shahril to make it 2-0.
Kedah temporarily reduced the deficit when Baddrol's free kick was headed into his own goal by Osmar Barba but the Spaniard managed to redeemed himself later in the match.
Osmar who was formerly on the books of Buriram United and Racing Satander, smashed home a free kick in the 63rd minute to restore his side's two-goal lead.
Seoul continue to dominate proceedings and eventually found their fourth on the night through Uzbek international Ikram Alibaev whoe curled in a sumptuous goal in the the second minute of added time.
It would be hard to say if the outcome would have been any different had Kedah kept 11 on the pitch but that is something that would probably keep Aidil and his players wondering in the immediate future.
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