Kovac's men take on Mexico at Arena Pernambuco in Recife knowing that they will likely need a victory to make sure of a place in the last 16.
Croatia were impressive in their 4-0 win over 10-man Cameroon on Wednesday and were considered unfortunate to come away with nothing from the tournament-opening 3-1 loss to Brazil nine days ago.
But, despite their strong performances in the competition so far, Kovac believes his team will need to improve in order to overcome Miguel Herrera's Mexico.
"I am pleased with the preparations for Mexico," Kovac said.
"We know everything about the opponent and now we hope that players will play just as well as in the first two games.
"Mexico is dangerous for their unity and their aggressiveness.
"When they lose the ball, they want it back in their possession as soon as possible. They won't change the style overnight, and there is already more pressure on them.
"I know what we need, but we have 90 minutes. From the first minute we will try to impose our rhythm, because that will make it easier for an early goal, but we will be patient.
"We have scored five goals in two games, had a few more opportunities, which shows that we play attractive and are a danger to the opposing goal.
"Already you have seen a shift in this short period of time and now we have to try and reach a higher level."
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