Pompey’s impressive impregnable defensive wall crumbled at the New Meadow upon their big examination.
Yet mistakes from Luke McGee and Matt Clarke should not topple the encouraging progress created by Kenny Jackett’s side.
The Blues had gone four matches without conceding heading to League One’s second-placed side.
As it turned out, two players so pivotal to their ongoing defensive strength would be the cause of the downfall and yield a deserved defeat.
In a tight fixture, with chances at a shortage, they were second-half slips so crucial to the 2-0 outcome at Shrewsbury.
McGee had already saved Simon Whalley’s poorly-struck penalty on 53 minutes, albeit having conceded it himself following a moment of indecision with Christian Burgess.
The Blues keeper sent Whalley sprawling as they briefly dithered when asked to deal with a ball over the top.
Still, McGee made the save – only to concede the opener six minutes later.
Jon Nolan’s shot struck Clarke and, in his attempts to trying to prevent a corner as the ball screwed wide, the stopper succeeded in only diverting the ball to Whalley.
The wide player did the rest, with a composed finish from the angle into the unguarded net.
Pompey never suggested they could rally with a leveller and on 81 minutes the contest was put beyond their reach.
Clarke was caught in possession 30-yards from goal and the ball found its way to substitute Stefan Payne, whose shot was partially saved by the exposed McGee but still found the net.
Clarke, the goal-scoring hero against Bury, beat the ground in frustration and it was hard not to feel his pain.
The central defender has been an outstanding presence this season, yet his slip sealed a first defeat in five for the team which has developed into play-off contenders.
Not that Pompey particularly deserved anything from the occasion, Shrewsbury were largely the better side and just desired the breakthrough.
Ultimately that was handed to them through a pair of uncharacteristic mistakes by a usually watertight defensive unit.
For the trip, Matty Kennedy was restored to the Blues’ starting line having found himself on the bench for the previous four matches.
And he would produce the only meaningful attempt on goal, Dean Henderson pushing out his first-half shot with more difficulty than perhaps it deserved.
His presence in place of Kyle Bennett was one of two changes to the team which beat struggling Bury at Fratton Park last weekend, with Ben Close coming in for the injured Stuart O’Keefe in midfield.
Yet there was a spark missing about Pompey’s play, despite getting to half-time injured, and they rarely threatened the Shrewsbury goal.
Fit-again Oli Hawkins did cause problems when he came off the bench in the 60th minute to replace Jamal Lowe.
Overall, however, the Shrews deserved their victory – and it was a win handed to them generously by two individual mistakes.
– NEIL ALLEN