Newport County boss Justin Edinburgh backed the decision to allow Mark Byrne’s winner to stand.
Pompey were incensed the 67th minute cross-cum-shot was allowed after the linesman had raised his flag for offside.
Despite Aaron O’Connor being in an offside position in front of keeper Paul Jones, referee Michael Bull saw fit to grant the goal.
It prompted a furious reaction from the visitors, with Jones booked for his protests as they went on to lose 1-0.
But Edinburgh,whose Exiles side are now third in League Two, is convinced the Chelmsford official got it right.
He said: ‘I don’t feel we had any luck with our goal, the laws being the law, it has to stand.
‘Aaron O’Connor wasn’t in the eye of the goalkeeper.
‘When I played the game it was offside but now it isn’t and credit to the referee for staying strong and making the correct decision.’
Byrne settled a tight contest played in front of a noisy Rodney Parade crowd.
Both sides struggled to carve out clear-cut opportunities, with little to choose despite the different league positions heading into the fixture.
Pompey should have been awarded a penalty after Byrne tripped Jed Wallace in the 40th minute but Bull waved play-on in another moment of controversy.
And Edinburgh admitted his team found it tough.
He added: ‘We had to dig in and get a result.
‘It was a competitive game that needed to be seen out and credit to Portsmouth, both sides went head-to-head and there wasn’t much room for moving the ball, it was a battle.
‘It is massive. We’ve ground out the win and taken six points off Portsmouth, who are the biggest club in this league.
‘To do that is a massive achievement for a club like us. We had to dig deep and work hard and will do so every week. It’s a massive achievement.’