Johnson's men are already guaranteed a play-off place but victory over his son Lee's Oldham side on Tuesday night would leave them two points off the automatic spots with two games remaining.
And given the unpredictable nature of the division Johnson believes a nine-point haul would give them a real chance of sneaking into the second tier for the first time in their history.
"If we are going to try to reach maximum points then we need to win our last three games and if we do get the 83 points then we are waiting for others to slip up," he said.
"We think 83 points will be close (to the automatic promotion places) so we must not let ourselves down and not get maximum points.
"We have to be in it to win it and make sure we are believing that a) we can win the next three games and b) there are enough teams out there who can beat the top teams which is happening all the time.
"We have got to be ready when that happens and not be the ones who fall away first."
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