Jemson struck in the last minute with the contest’s only goal to send 2,500 PNE fans wild in the away end.
The teenage striker was back with North End at the time on loan from Nottingham Forest, a £250,000 move having taken him from Preston to Forest the previous year.
Lilywhites manager John McGrath had brought him back before the late March transfer deadline to give the play-off push a kick.
This goal did just that, putting daylight between them and Chester who were rivals for the top six.
For whatever reason his return had not been greeted with too much enthusiasm by some of the PNE faithful but his popularity rocketed in a swing of the boot.
How it took PNE so long to make the breakthrough was something of a mystery.
They had bossed the game and had enough chances to win it, something even Chester manager Harry McNally conceded.
“Preston were three goals better than us and we could have no complaints whatsoever,” said McNally.
“We never got near enough to their defence to test them out.”
This was only Preston’s fifth away win of the season and despite the narrow margin of victory, it was their best display on the road.
They’d just come out of a four-game run without a win, beating Notts County 3-0 at Deepdale the week before.
This was a fine follow-up, forming part of a six-match unbeaten run through to the play-offs.
North End wore red socks with their yellow away kit for the occasion, in honour of the Liverpool fans who had died in the Hillsborough disaster the week before.
Former Liverpool winger Brian Mooney had a fine game and could have finished with a hat-trick.
The Irishman hit the bar with a 30-yard shot, forced goalkeeper Billy Stewart into a fine save and watched as defender Colin Woodthorpe cleared an effort off the line.
The first half in the main was quite even, Warren Joyce sending a shot too high and Stewart twice saving from Neil Williams.
However, the second half belonged almost exclusively to PNE, with them launching wave after wave of attacks.
There was a scare in the 66th minute though, Chester striker Carl Dale breaking clear. North End keeper David Brown was equal to the 22-goal striker and made a vital block.
Bob Atkins and Williams had chances before Jemson broke the deadlock with 89 minutes played.
Atkins struck a low drive from outside the box which Stewart dived to parry.
Stewart then blocked Joyce’s follow-up, the ball breaking loose to Jemson who turned it home from six yards to the delight of the PNE fans behind that goal.
Preston: Brown, Williams, Atkins, Hughes, Wrightson, Swann, Mooney, Joyce, Harper (Bogie), Ellis, Jemson. Sub (not used): Miller.
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