Wigan Athletic 1 Preston 2
North End took the lead inside seven minutes, with Tom Barkhuizen tapping home at the far post after good work from Ben Pearson and Daniel Johnson.
After being thwarted on a couple of occasions by Scotland No.1 David Marshall, Johnson doubled the lead three minutes after the restart with a fine finish to another well-worked move.
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Hide AdThat was the cue for Paul Cook to send on Gelhardt and Michael Jacobs for Lee Evans and Tom Pearce, and switching from five at the back - which hadn't been working - to four.
And within seconds of his arrival, Gelhardt created a goal for Latics, with his cross finding Kieffer Moore before Chey Dunkley lashed home from close range.
Then, with seconds of the 90 minutes to go, Gelhardt drilled in a near-post effort that was brilliantly saved by Declan Rudd.