Joachim Low's side have been praised for the exhibition of attacking football in the 7-1 thrashing of Brazil in the semi-final, but Mertesacker is certain that will be forgotten quickly if they do not produce a similar display against Argentina.
"Our performance against Brazil was nearly 100%," the Arsenal defender told reporters. "If you look at the stats, the passing, the goals we scored, everything was so fluent.
"We played a good match with Brazil but we have to show another game with the same attitude, with the same focus.
"That's needed in the final, otherwise we have no chance. If we drop 5% then we have no chance."
Mertesacker is likely to start the match on the bench if, as expected, Mats Hummels shakes off a knee injury to take his place in the centre of defence.