I wouldn't like to underestimate South Korea but I believe that they have a really challenging group in the World Cup. Even Ghana would put up a good fight against them I think. But let's say that they defeated Ghana, I still don't think that they can qualify for next stage of the tournament. Portugal and Uruguay are way stronger teams than them. Maybe we don't have the prime Portugal but they are still strong now. Even if they don't end the group stage as the leader, they would end as the second.