Conor Chaplin struck the winner for Pompey with his first touch after coming on as substitute as Pompey claimed a 2-1 win at league leaders Northampton.
The young striker was on hand to tap home a rebound from close range four minutes from time after fellow sub Ben Tollitt had led a swift counter-attack from a Northampton corner.
Pompey had to come from behind to pick up the victory but dominated most of the second half, without ever really finding the clear chance to take the points.
The Blues found themselves 1-0 down in the 17th minute moments after a lucky escape.
After Adam Webster slipped to allow Marc Richards clean through on goal, Brian Murphy then produced a fine save in the one-on-one to deny him.
But from the resultant corner, the Blues keeper was then unable to do anything about Ryan Cresswell’s powerful header as the league leaders broke the deadlock.
Pompey had shown some menacing moments without really troubling the Northampton keeper but produced a moment of quality to grab the equaliser just beyond the half-hour mark.
Marc McNulty set off on a run from the halfway line towards the right flank and his inviting cross was met with a bullet header from Gareth Evans that flashed high into the net.
And although Paul Cook’s side looked the more threatening in the second half, Town always looked a danger from corners until Chaplin’s late effort sealed the points.