Blues beaten at Globe Arena
Pompey made the long trip home from Morecambe disappointed after suffering a first league defeat of the season.
They were poor in the first half and the hosts took advantage with goals from Ryan Edwards and Tom Barkhuizen.
There was a marked improvement after the interval, but a string of fine saves from Barry Roche kept the Blues at bay.
Paul Cook made three changes from the side that drew with Crewe at the weekend.
Enda Stevens recovered from the groin problem that kept him sidelined at Alexandra Stadium to replace Kal Naismith at left-back.
Adam Barton came in for the injured Jack Whatmough in the centre of defence, while Milan Lalkovic dropped to the bench to make way for Kyle Bennett.
Pompey made an encouraging start, with Stevens and Drew Talbot sending in a couple of dangerous deliveries that the hosts were able to clear.
But Morecambe soon settled and a free-kick from skipper Michael Rose had to be cleared by his namesake Danny.
Cole Stockton then cut along the edge of the Blues box and fired in a shot that hit Christian Burgess and looped over the bar.
Pompey were being allowed to see plenty of the ball and were not having any trouble getting into the opposition half, but were struggling to get through the defence and test Roche.
And the Shrimps were looking an increasing threat on the counter-attack before they broke the deadlock after just 10 minutes.
The visitors failed to deal with a ball in from the left and it fell kindly for Edwards to hit through a host of bodies and into the net.
It was becoming a familiar story at the other end of the pitch, with plenty of teasing crosses, but no end product.
Morecambe, meanwhile, were looking far more clinical and broke quickly upfield after Carl Baker had a penalty appeal turned down to double their advantage.
It was a fine finish from Barkhuizen that flew past the grasp of David Forde and into the top corner, but he was allowed far too much space to burst forward.
Roche was finally called into action on 25 minutes, just about beating Baker to the ball as the midfielder tried to latch onto Bennett’s incisive pass.
Michael Smith then rose highest in the box to meet another cross from Stevens, but could only glance his header wide.
They failed to build on that spell of pressure, however, and instead almost fell further behind.
Barkhuizen ran into the box from the right and lifted the ball over Forde, only to see the ball hit the side netting.
Half Time: Morecambe 2 Pompey 0
Baker was trying to be positive at the start of the second half and hit a couple of efforts that did not really trouble Roche.
He certainly made a clean connection on 52 minutes, though, hitting a fierce effort that Roche did well to turn behind.
Baker was single-handedly trying to bring the Blues back into the contest and his next attempt flashed narrowly past the post.
Pompey were looking a lot brighter since the restart and Barton twice found himself in the opposition area to have shots that were deflected wide.
Cook tried to keep the momentum flowing by making a double switch on 64 minutes, with Smith and Bennett making way for Curtis Main and Lalkovic.
But it was Roberts who soon had a chance to reduce the deficit with a firm low drive that Roche managed to get a hand to and palm clear.
And the Shrimps stopper made an even better save soon after, somehow keeping out a Main header from point-blank range.
Then, after Lalkovic was fouled 30 yards out, Baker stepped up to curl a free-kick over the wall, but also over the bar.
Pompey were totally dominant, with Morecambe unsurprisingly content to sit back and soak up pressure.
But they were indebted to Roche, who added to his tally of super stops by denying first Main and then Burgess.
The keeper was not done yet, flinging himself to his right on 82 minutes to keep out a free-kick from Roberts that was heading for the top corner.
Noel Hunt replaced Rose for the closing stages as Cook made one last attacking throw of the dice.
But that failed to spark an improbable late comeback as Pompey’s wait for a first win of the campaign continued.
Morecambe (4-2-3-1): Roche; Wakefield, Edwards, Whitmore, Conlan; Fleming, Rose (c); Barkhuizen (Kenyon 87), Dunn (Molyneux 60), Ellison; Stockton (Mullin 75)
Goals: Edwards 10, Barkhuizen 21
Booked: Stockton, Fleming, Molyneux
Subs not used: Nizic, McGowan, Turner
Pompey (4-2-3-1): Forde; Talbot, Barton, Burgess, Stevens; Rose (Hunt 85), Doyle (c); Baker, Roberts, Bennett (Lalkovic 64); Smith (Main 64)
Booked: Doyle, Stevens
Subs not used: O’Brien, Buxton, T.Davies, Linganzi
Referee: Nigel Miller
Attendance: 1,838 (546 Pompey fans)