Ronan Curtis extended Pompey’s lead at the top of the League One table to three points with a stunning effort to settle the Blues’ trip to Coventry.
The Irishman made the most of a Brett Pitman knockdown in first-half stoppage-time to defy keeper Lee Burge’s out-stretched hand and extend Kenny Jackett’s side’s unbeaten start to the season to 11 games.
It was the Republic of Ireland international’s sixth goal this term as he once again proved a key factor in the Blues’ ongoing bid to return to the Championship.
In a bitty first half, where both side’s attempted to stamp their authority on proceedings without achieving their objective, three moments stood out amongst the scrap.
Ben Close could have handed the Blues the perfect start when on six minutes Jamal Lowe and Nathan Thompson combined well to hand the midfielder a clear sight of goal.
But rather than burst the net from 15 yards out, he fired wide to hand the Sky Blues a massive let-off.
Pompey themselves breathed a huge sigh of relief just after the half-hour mark when a mix-up at the back gifted Jonson Clarke-Harris the chance to put the home side in front.
Matt Clarke misjudged the pace on Jack Whatmough’s backward pass and the centre-half hesitated.
That allowed Clarke-Harris to nip in and steal possession - yet Blues keeper Craig MacGillivray was alert to the danger as he raced off his line to deny the Coventry front man.
A stalemate looked the likely outcome going into the break - but that was before Curtis’ timely and mouthwatering intervention in first-half injury-time.
Gareth Evans won possession in the middle of the park to present Close with the chance to choreograph a Blues chance.
He picked out Pitman, who headed the ball into the Irishman’s patth, and he did the rest by curling the ball beyond the reach of Burge to hand Kenny Jackett’s side the lead.
There was a sense of urgency about the hosts as the second half kicked off.
But as Pompey did well to manage the situation, the restlessness among the natives was gaining strength.
The introduction of substitute Jodi Jones appeared to give them renewed hope - yet with Pitman drawing a save out of Burge just before the hour mark, it was the Blues who posed the greater threat going forward.
The 1,961 away fans in attendance were in fine voice as the match’s finishing line came into sight - even when Lowe sliced his effort spectacularly wide with 82 minutes on the clock.
A pile-driver from substitute Ben Thompson heightened expectations of another impressive performance on the road.
And even though Naylor had to be alert to clear off the line to deny Coventry a late equaliser heading into injury-time - there was a real sense the hard work had already been done.
That faith was repaid minutes later when referee Brett Huxtable blew the final whistle - and oh how the away fans celebrated as their team delivered to keep their ambitions of promotion firmly on track.