Promotion-chasing Pompey dropped to fifth in the League Two table - and missed the chance to put more pressure on the top three - after falling to a 1-0 home loss to Exeter today.
David Wheeler’s fortuitous second-half strike settled matters on the south coast, with the lacklustre Blues, who began the day in fourth, far from their best.
Third-placed Carlisle drew at home to Barnet, meaning a win would have put Paul Cook’s side one point off the top three with a game in hand had they claimed victory.
As it was, defeat for the Blues meant Luton’s win at Cambridge dropped them into fifth spot in the table.
The first half started brightly for Pompey who were quick out the blocks and threatened an early breakthrough when Conor Chaplin’s back-heel flick from Carl Baker’s low cross flashed wide of the near post.
The hosts then fashioned another good opportunity to open the scoring when Enda Stevens’ deep cross found the head of Michael Smith - but the front man was unable to keep his effort on target.
That, though, was about as good as it got for the Blues in the opening 45 minutes, with in-form Exeter growing into the game.
Attacking duo Reuben Reid and Ollie Watkins provided a constant threat, with the latter presented with the best chance of the half when he got on the end of a counter-attack, only to fire his right-footed shot narrowly past David Forde’s post.
Reid, who was enjoying a good battle with Pompey defender Christian Burgess, was also denied the opener when David Forde saved at this near post – gathering the ball at the second time of asking.
Neither team, though, deserved to be ahead at the interval, with the score goalless at the break.
The first chance of note in the second half brought the breakthrough for Exeter in the 57th minute.
And it was very harsh on the Blues, with the visitors making the most off a huge slick of luck.
Reid’s marauding run had been ended, but with Matt Clarke keen to clear his lines for the hosts, his clearance hit Danny Rose, with Wheeler on hand to slam home from close range.
Cook reacted immediately to falling behind with Smith and Baker taken off for Jamal Lowe and Gary Roberts - Smith’s withdrawal ironically cheered by some fans.
Lowe certainly gave the Blues a boost with a couple of exciting runs showing the home side’s intent.
Right-back Gareth Evans had the best chance of a quick leveller, though, when he brought the ball down well on the edge of the box before firing a left-footed half-volley that was saved well by Pym in the visitors’ goal.
The game became very open in its nature owing to Pompey’s need for a leveller and Exeter were almost able to take advantage of that by winning a corner on the counter-attack.
Troy Brown, however, was off target from close range before Forde and Reid came to a heated disagreement in the area with both booked for their part in causing an unnecessary melee.
With time ticking down, Enda Stevens tumbled in the box but half-hearted appeals were turned away.
And despite a flurry of late corners in five minutes of added time, and two Naismith efforts, the Blues were beaten.