Pompey were blown away in the opening 18 minutes as they tumbled out of a second cup competition within 72 hours.
Roared on by a vociferous home crowd, Newport grabbed two goals in a blistering start to last night’s game.
The shell-shocked Blues had no answer.
It put Guy Whittingham’s wilting side on the way to a poor 3-0 defeat at Rodney Parade.
They exited the Johnstone’s Paint Trophy with a whimper – and deservedly so.
In a painful spectacle for visiting supporters, Conor Washington netted in the fifth minute, after a calamitous mix-up between Bondz N’Gala and Trevor Carson.
Another abject goal conceded this season was added to in the 18th minute.
Deji Oshilaja headed home after Carson had saved well from a free-kick.
It took until around the 35th minute before the Blues finally got a foothold in the match.
But the damage had already been done and they were on their way out of the competition.
County skipper David Pipe was sent off in the 67th minute for an awful challenge on Ricky Holmes to at least provide an glimmer of hope there may be some way back for the lacklustre visitors.
Instead, Washington grabbed his second of the game in the 82 minute to seal a comfortable Newport win, despite their numerical disadvantage for the final 23 minutes.
For Pompey, it follows Saturday’s FA Cup elimination to Stevenage.
Last night the makeshift side were well beaten in an embarrassing display at a team with 10 players out injured.
Whittingham made five changes to the side who lost at Stevenage in the FA Cup at the weekend.
Johnny Ertl, Patrick Agyemang and Yassin Moutaouakil were all rested, the latter two not making the 16-man squad at Newport.
With Jed Wallace and Gavin Mahon also suspended, there were first-team returns for Ricky Holmes, Shaun Cooper, Danny East and Romain Padovani.
Cooper and Padovani formed a new-look central midfield, with East slotting in at left-back to allow skipper-for-the-night Joe Devera to move over to right-back.
Meanwhile, Tom Craddock was back in the side for the first time since the second game of the season, following a frustrating run of injuries which have restricted his impact.
Simon Ferry and Thery Racon were absent through injury for the second match running.
When play got under way it took just five minutes for Newport to break the deadlock, albeit in calamitous circumstances.
The ball was played down the right-hand side of the box and as Carson rushed out to collect in the air, N’Gala headed it instead.
It left the keeper stranded and Washington had the opportunity to slot the ball home from a tight angle into an unguarded net.
The hosts continued to put Pompey under pressure and after some desperate defending Whittingham’s men were relieved when Danny Crow slashed the ball wide.
Padovani had the Blues’ first attempt on goal, when in the 12th minute he lashed a 25-yard shot from distance comfortably wide.
Moments later, the pace of Washington left Devera struggling down the left but his cross, intended for Christian Jolley at the far post, was plucked out of the air by Carson.
The lead was extended in the 18th minute, after Padovani had initially fouled Jolley 22-yards out, earning him a booking.
Robbie Willmott’s free-kick was well saved by the fingertips of the flying Carson but Oshilaja was on hand to head the loose ball into the net.
It was relentless from County and in the 27th minute Cooper’s loose pass in the centre of midfield was picked up by Willmott who drove a long-range shot narrowly over the bar.
Another Newport corner then sparked a scramble inside the penalty area, prompting a block by Carson and amid a flurry of bodies the keeper then emerged with the ball in his grasp.
In the 35th minute there was more suicidal play from struggling Pompey.
East’s attempted back pass to Carson instead gave Crow a glimpse of goal.
But the keeper slid in to tackle and then clear.
There was a response from the Blues, though.
Firstly Ryan Bird headed a Holmes cross over, followed by Holmes himself seeing a low shot saved after an excellent team build-up.
Cooper next drove in a right-foot shot, low from 25-yards, which saw keeper Jamie Stephens manage the slightest of fingertips to nick it around the post.
Whittingham elected not to make any substitutions at the interval but within nine minutes of the restart David Connolly was introduced for Craddock.
Moments later Bird should really have done far better with a headed opportunity following a great cross from Cooper down the right.
Instead the contact was minimal.
Padovani then lashed in a ferocious first-time 30-yard shot which was brilliantly saved by Stephens, with Connolly adjudged to have been offside as he attempted to turn home the rebound.
In the 67th minute, Pipe was shown a straight red card for a wild two-footed lunge on Holmes on the left-hand touchline to give the visitors hope.
But it was Washington who ensured there would be no late doubts, turning Devera before firing home on 82 minutes to secure County’s progress into the next round.