The 42-year-old was thrilled to see his side bounce back from a cruel defeat to Brazil with the most convincing of victories on Wednesday night
A goal from Ivica Olic before the break gifted the Croatians the lead before Ivan Perisic and Mario Mandzukic (2) put the match to bed in the second half, much to the satisfaction of Kovac.
"We weren't on top of our game in the opening five to 10 minutes and Cameroon created some chances," Kovac told HTV.
"But then we found our rhythm. Olic scored and that opened up the game for us. We could have scored even more goals.
"I can only congratulate the players, though. They won in very difficult conditions. It was hard to sit or stand, let alone run around on the pitch."
Kovac then looked ahead to the decisive game against Mexico and warned that a Croatia will have to be at their best in order to progress.
"The match against Mexico will be like a final. We have to get some rest, because a serious opponent awaits. Mexico are strong, but so are we.
"The Mexico players are very patriotic, just like us, and they have a great team spirit. They play some aggressive football with a lot of pressing. They are strong going forward, but also have some weaknesses in defence, like Brazil showed us."
Croatia currently sit third in Group A with three points from two games, trailing leaders Brazil and Mexico by one point.