The quarterfinal first leg ended 1-1, so Juve could draw 0-0 and qualify, a different approach to the fightback from 2-0 down to beat Atletico Madrid.
Allegri said, “The first leg result is irrelevant. We must play with the same intensity we did against Atletico Madrid. We must have great respect for Ajax and also move the ball with much greater precision than we did in Amsterdam. If we do those two things, we can go through.
“The game will always be open, because we'll both play to win until the bitter end, so it won't be over until the final whistle.
“It'll be an important night for an extraordinary target, reaching the semi-final, so we need the fans to push the lads on to achieve it. There will be times when we need to defend and we have to do it all together."