Even if Palace get an early goal, the City manager believes that Robins supporters will remain behind their team.
"They will keep positive," he said. "How many times have they seen us score in the last minute over the last couple of years?
"It's when they get going they know the players get going so they do play a big, big part in that.
"The more often something happens, the more people believe in it and we've got to show a fantastic position of strength both on and off the field.
Johnson has learned a lot about what motivates his team over the last two seasons. And, most importantly, he believes they have got their game back together at just the right time.
Interview: Bristol City striker Lee Trundle
City's 3-0 win at home to Preston on the last day of the league campaign was their first in five games. And just what it did for confidence was illustrated by Saturday's 2-1 win at Selhurst Park.
"We had great form at the start of the season," said Johnson. "I think we'd lost one in 14, and that was Palace's form at the end of the season.
"Everyone finds their form at some stage and loses it at some stage.
"Over 46 games it will even itself out but, over two or three games, you've got to find it because you don't get another chance."
Johnson also insists that the play-offs will be the acid test of whether he has brought the right blend of players to the club.
"When a manager brings a group together I think the personalities are very important," he said. "Before the Palace game I really felt this was my chance to see if I had brought the right people to this club."
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