A 1-0 defeat to Sweden in their opening Group F clash at the Nizhny Novgorod Stadium on Monday has immediately put the Asians on the back foot and needing an improved performance against El Tri, by their own admission.
"To be fair, every team in our group is better than us, so every game is going to be tough," the midfielder said as he looked ahead to Saturday's encounter in Rostov-on-Don.
"I watched Mexico's game against Germany and, as I expected, they looked a really good team, really good organisation and their individual performances were great."
Mexico upset the world champions with a fully deserved 1-0 win in Moscow on Sunday.
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"It is going to be an even tougher game. Sweden had bigger players and used more their physical size but I expect Mexico to play more with the ball. They are faster, so it will be a different kind of game," Ki added.
"We have to focus on our defensive side first so that we don't concede and then maybe we can get something on the counter attack or from set pieces."
Ki, who has announced he will leave relegated Swansea City after five seasons at the Welsh club, suggested all was not lost for the Koreans.
"Our organisation was not that bad in the game. We had chances as well, so it was disappointing (to lose). We could have won, it could have been a draw but Sweden won in the end and I suppose that was a fair result," he added.
"In this tournament the first game is always crucial."
(Editing by John O'Brien)
