Kal Naismith was the Pompey hero as his late strike earned Pompey a 1-0 win at Grimsby.
The substitute climbed off the bench to claim all three points for Paul Cook’s side with a winner four minutes from time.
After dominating the match, the Blues got their reward on 86 minutes when Carl Baker was brought down and, from 25 yards out, Naismith whipped a free-kick into the right-hand corner to send the away fans and Pompey staff wild.
The victory is Pompey’s second successive away win and keeps them fourth in League Two.
It was one-way traffic in the first half as the Blues dominated possession but failed to create any clear-cut chances.
In a bright opening, Kyle Bennett twice went close with efforts that were tipped out for corners by keeper James McKeown.
Baker got in on the action with the best chance of the half on 21 minutes.
The midfielder did well to wriggle clear on the edge of the area but his low right-footed drive was too close to McKeown.
Just past the half-hour mark, Enda Stevens cut a path into the area and his centre was scrambled away by a panicked Grimsby defence.
Pompey picked up where they left off after the interval. Smith ‘s shot lacked power after he was played in by Christian Burgess.
The forward was then inches away from Bennett’s fierce left-wing delivery, moments before a Stevens pinpoint cross into the six-yard box evaded a blue shirt.
Grimsby gave Pompey a warning on 54 minutes, though, as Ashley Chambers picked up possession after a long throw and his whipped shot from the edge of the box had to be clawed away by a scrambling Forde.
The Blues kept on plugging away but, just as it looked to be another frustration afternoon of dominance but no victory, Baker was brought down by Jackson.
And up stepped Naismith with a classy set-piece to hand all three points to Paul Cook’s men.
Pompey: Forde, Evans, Burgess, Clarke, Stevens, Rose, Doyle, Baker, Roberts (Naismith 76), Bennett (Chaplin 76), Smith (Hunt). Subs: O’Brien, T Davies, Lingazi, Lalkovic.
Grimsby: McKeown, Andrew, Gowling, Chambers (Bolarinwa 58), Bogie, Mills, Jackson, Berrett, Summerfield, Collins, Comley (Vernon 72). Subs: Pearson, Disley, Venney, Boyce, Henderson.