Changes were made after the midweek win away at Middlesbrough. Nemcha, Stockley and Maguire all featured in a three pronged attack. Robinson was also back on the bench as Preston enter the last phase of the season.
The game was limited in terms of chances. This was partly down to the horrible weather conditions with a strong wind and heavy rain throughout the game.
North End were strong at the back. The recent partnership in the centre has matured and this has combined with Preston's unbeaten run. The home side were difficult to break down.
The visitors did have the better of the chances in the first half. Just before the break Birmingham were on the attack when a shot was curled wide when it was probably easier to score.
Preston played better in the second half but neither side could find a breakthrough despite various substitutions until the very end of the game.
Johnson curled in a corner which Maguire ran onto and headed home. It was the 94th minute and there was no time for Birmingham to respond.
The three points meant Preston moved into seventh place level on points with Aston Villa and a further point behind fifth placed Middlesbrough.
The international break now takes place but Preston will return for their final eight games at the end of the month as one of several teams in with a shout of claiming the last two play off places.
North End do have a very tough April facing a number of the top sides but they have at least put themselves in with a chance of making the top six after being int he bottom half of the table in January.