Skipper Matt Mayes struck in extra-time to power Pompey Academy past Gillingham in the FA Youth Cup first round.
The striker pounced on Oscar Johnston’s pass to fire home a vicious right-foot shot in the 103rd minute and seal a 2-1 triumph for Mikey Harris’ side.
It finally separated the teams, who had fought out a 1-1 in normal time at the Priestfield Stadium.
The Blues’ youngsters had found themselves behind after Leroy Hlabi’s third-minute penalty, representing a disastrous opening.
But Mayes levelled on 26 minutes when Gills keeper Louie Catherall pushed the ball against the forward’s head and it found the net.
The lively second-year scholar also struck the bar early in extra-time as the game opened up.
He made no mistake, however, later in the first period, to book the Academy a home fixture with non-league Lewes.
Pompey found themselves behind after only three minutes as the hosts registered with a penalty.
Hlabi made a pest of himself, poking the ball through the keeper’s legs on the byline and, as he headed towards an open net, Matt Casey brought him down.
The Blues’ towering centre-half received a booking, while from the spot Hlabi sent Jack Collins the wrong way with a right-foot finish.
The Gills could have doubled their lead on 11 minutes when Collins failed to hold Jack Conway’s angled shot and Casey was forced to hack clear.
However, the ball fell invitingly to Jason Gildea just inside the box, but he flashed a right-foot shot well over the bar with the visitors in disarray.
Then Collins tip superbly to get the faintest of touches to tip over Thomas Bramble’s header from Henry Arnold’s cross from the left.
But the match was all-square on 26 minutes through a piece of good fortune for Pompey.
Leon Maloney’s delivery from the left was pushed out by keeper Louie Catherall and into the face of Mayes, before the ball ricocheted into the vacant net.
The Blues’ skipper had to receive treatment, but was able to continue as his team attempted to build on their leveller.
At the interval, with the scores level, Pompey introduced Brad Lethbridge for James Whiting.
The second half began in lacklustre fashion, with neither side impressing, although Collins was called upon to claim a flying take from Ryan Huckle’s attempt following a corner.
There was a moment of controversy in the 72nd minute when Miguel Scarlett broke from defence into Pompey’s penalty area and went down under a challenge from Read.
However, referee Damith Bandara elected to book Scarlett for diving and no spot kick was forthcoming.
With the scores still level after 90 minutes, the match entered extra-time and within three minutes Mayes’ deflected effort struck the bar, with Lethbridge sending the follow up wide.
But in the 103rd minute the goal arrived.
Substitute Johnston did superbly down the right and slipped a ball inside the box which was met with a ferocious first-time right-foot finish from Mayes.
The Gills’ Henry Woods was sent off on 117 minutes for something he said to the referee - and Pompey eased to their victory.
Pompey: Collins, Brooks, Casey, Dandy, Chandler (83 mins Johnston), Hancott (106 mins Flint), Whiting (46 mins Lethbridge), Read, Smith, Mayes, Maloney.
Subs Not Used: Pitman, Mnoga,.
Gillingham: Catherall, Scarlett, Arnold, Bramble (84 mins Arthurs), Huckle, Tucker, Woods, White, Hlabi, Gildea, Conway (117 mins Laing).
Subs Not Used: Walsh, Sheminant, Noyelle.