Pompey moved into the last 16 of their EFL Trophy defence after coming from behind to defeat Northampton at Fratton Park.
Leon Maloney bagged his maiden Blues goal to cancel out Michael Harriman’s opener before Marcus Harness crashed home the match-winner in the second half.
It ensured Kenny Jackett’s men booked their spot the third round of the competition they won last season, while they made it six successive wins in all competitions.
Pompey made nine changes from Saturday’s FA Cup victory over Altrincham on Saturday.
Ross McCrorie made his return from a hamstring injury to start in central midfield along with Andy Cannon.
Brett Pitman was back skippering the Blues, while forgotten-men James Bolton and Paul Downing were also recalled to the defence.
Pompey made a slow start to the game, with Matt Warburton forcing a decent save out of Alex Bass.
On six minutes, Marcus Harness conjured up a superb piece of skill down the right and crossed for Pitman, whose header back across goal was cleared by the visitors.
Then the deadlock was broken in the 12th minute by the League Two Cobblers.
Joe Martin’s crossed from the left and Harriman ghosted in from the back post to head home unmarked from close range.
Things almost got worse for the Blues after the restart but Harry Smith dragged his 25-yard effort wide.
Jackett’s men slowly improved, however, and Gareth Evans forced a decent save out of Northampton keeper Steve Arnold on 18 minutes.
And Pompey were finally level six minutes before the break through Maloney’s first goal for the club.
The fledgling winger bravely stooped low to meet Harness’ cross and headed home via a deflection.
The home side started brightly in the second half, with Pitman having a header clawed out by Arnold.
On 50 minutes Warburton cracked a long-range shot but it was down the throat of Bass.
The game started to open up, with Bass then saving well from Harry Smith and then Warburton.
Then Pompey started to create their own opportunities, with Pitman heading wide on two occasions.
The Blues started to press their foot on the gas and finally got their rewards. Evans’ centre could be cleared only as far as Harness and he thumped home an outstanding volley to put Jackett’s troops in front.
Pompey continued on the front foot, with Pitman having a heading superbly kept out by Arnold.
Moments later the former Bournemouth marksman bent an effort just the wrong side of the post after neat play between Harness and substitute John Marquis.
It was all Pompey in the closing stages, with Arnold denying Marquis with an excellent save when Brandon Haunstrup pulled a cross back.
The Blues saw it out comfortably and ensured they’ll be in the hat for Thursday night’s draw.
More impressively, that’s six wins on the trot and Jackett’s men have suffered just one loss in 14 games.
Pompey: Bass, Bolton, Downing, Raggett, Walkes, Cannon (Close 86), McCrorie (Haunstrup 63), Harness, Evans, Maloney (Marquis 63), Pitman.
Subs not used: MacGillivray, Burgess, Williams, Harrison.
Northampton: Arnold, Hall-Johnson, Turnbull, Wharton, Harriman, Watson, McWilliams (Waters 51), Watson, Martin (Williams 68), Warburton, Smith (Harding 68).
Subs not used: Cornell, Kaja, Hughes, Ballinger.