PNE, in truth, battered the Humberside club who arrived at Deepdale chasing promotion.
The Tigers were lucky not to lose by more as Steve Bruce's team – who would go on to win promotion at Wembley after a third-place finish – were left counting themselves lucky to still be in the game when Abel Hernandez nearly snatched a late equaliser which was deemed not to have crossed the line.
Hull had recently secured a big win over Burnley.
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But sporting players who would go on to become current football superstars – such as Scotland captain Andy Robertson and Manchester United skipper Harry Maguire – they were no match for the Lilywhites on the cold winter's day.
Despite bombardment from start to finish, including 11 first-half shots, it was a set-piece that found the breakthrough for Simon Grayson's side.
Daniel Johnson rolled the ball into Gallagher's path and his strike found the back of the net.
North End started the game quickly, Adam Reach had two attempts within minutes, as they reinforced why they were the top home scorers in the Championship so far.
A timely block prevented Joe Garner getting a shot on target after selfless play from Will Keane.
Then Garner forced two saves from McGregor and Gallagher tried his luck from distance.
Hull were struggling to cope with the hosts' intensity and should have fallen behind in the 14th minute, when Garner took a touch away from danger only to blaze over from six yards out.
Robert Snodgrass curled over on a rare Hull foray forwards, before Shaun Maloney put his team-mates in trouble at the other end.
The Scotland international's poor pass was lapped up by Keane and the Manchester United loanee fired across the face of goal, much to the annoyance of team-mate Garne,r who made sure his strike partner knew what he thought of the decision to go it alone.
Tom Huddlestone's half-time introduction brought about a threat for Hull with the substitute forcing Jordan Pickford into a fine save down to his right.
Chuba Akpom found the net moments later, unaware the offside flag had been raised, as Hull had improved in the second period, albeit North End were still proving a threat.
Gallagher and Reach attempted to find an opener, which arrived in the 66th minute after Huddlestone was adjudged to have fouled Garner on the right flank.
Johnson’s smart free-kick across the face of goal was turned home by Gallagher as the crowd of bodies went towards goal .
Deedpale erupted in relief as well as celebrations, as did the players, but it was not over just yet.
Reach had an effort cleared off the lined by Maguire before the match ended in controversial fashion as City were denied a last-gasp leveller.
The officials adjudged the ball to have been scrambled away before it had crossed the line, as Hernandez’s effort was blocked by John Welsh.