Mata struck a late goal after David Villa and Fernando Torres had also found the net as the current world champions bowed out of Brazil with a convincing victory over Ange Postecoglou's side.
However, the Manchester United star says the win does little to repair the damage of their opening defeats to Netherlands and Spain and admits Vicente del Bosque's men were found out by their opponents this month.
"We wanted to get a better shape of ourselves and we did it. Anyway, this last game doesn't fix this World Cup," he told Telecinco after the match.
"The only reasons to explain our elimination are football. People talked about many things - discrepancy with Del Bosque - but I don't think so. The other teams were better than us, they knew how to defend against us and football is like this. You lose two games in a row and you are out.
"What is now said about the renewal in the national team... we are all used to it and it's normal when you're used to winning and in a specific moment you don't. The coach knows the reason is just football, though. We didn't play to our level and that's all."
"We have met our goal for today," said the Real Madrid man. We had to finish in the best possible way, we had to win and the taste is not the worst.
"The past is past and we have to face the future in the best possible way, with pride and dignity. We leave the World Cup with sadness, though. The World Cup is over now and we have to think of the goals ahead next season.
"I'm just thinking about resting. What needs to come in the future will come"