Will Grigg scored a brace after coming off the bench at Rodney Parade
Chesterfield made it six unbeaten in League Two as they recorded a first win at Newport County in 55 years.
The visitors made the most of some atrocious Newport defending to triumph, with Dilan Markanday opening the scoring after just 42 seconds.
Will Grigg added two more late on to make it three defeats on the bounce for the Exiles.
Home supporters voiced their frustration at head coach Nelson Jardim, whose side now have the worst defensive record in the division with 24 conceded from their opening 12 games.
Such fragility may have been sensed by the Spireites who could not have asked for a better start.
A hopeful ball in the very opening exchanges was chased hard by Markanday - and inexplicably not dealt with by neither defender Kyle Jameson nor goalkeeper Nick Townsend.
Amid the confusion, Markanday was calm to finish from the edge of the area into the empty net, the on-loan Blackburn forward's fourth goal in seven games.
Newport did not threaten themselves until after making half-time changes in a low-quality affair – and even then Courtney Baker-Richardson blew their best chance when he failed to connect with a low Noah Mawene cross on 63 minutes.
Home fans protested on 73 minutes when they thought Spirites keeper Max Thompson carried the ball over his own line as he attempted to catch a tricky corner.
Having been spared his blushes then, two minutes later Thompson was saved by the woodwork as Kyle Hudlin’s cross hit the post.
But Chesterfield sealed things as substitute Grigg slid home to meet Ollie Banks’ low centre on the counter five minutes from time.
If Newport’s defending was hesitant on that occasion, it was horrendous three minutes later as they failed to contain Grigg, who shook off markers to turn and scruffily bobble the ball past Nick Townsend for the striker’s sixth of the season.
Newport County head coach Nelson Jardim told BBC Sport Wales: "It is frustrating. The way we started the game was just bad.
"We were then trying to get ourselves back into the game, but we didn’t find the best ways of doing it.
"In the second half with the changes we made I think we improved the team and created goalscoring chances and we’re unlucky we didn’t take at least one.
"Everyone is telling me it’s a goal, the players, some of the staff... and in that moment we were on top of the game and we had more energy to score a second. We didn’t and I think we paid a big, unfair price
"We lost a little bit of focus trying to get the draw and those two goals came in an unfair way. Speaking with (Chesterfield manager) Paul Cook, he agreed 3-0 was a bit unfair for the effort the boys made."
Chesterfield assistant manager Danny Webb said: "The early goal was obviously a mistake from them, but it summed up Dilan Markanday’s performance by chasing down a potential lost cause.
"That set the tone and it’s a big help going 1-0 up within a minute away from home against a really loud home crowd – it just kills the whole vibe a little bit.
"In the second half they really started to bombard our box and everyone had to pitch in defensively.
"Fair play to Newport, they threw everything at it to try to get an equaliser. But Max was excellent in goal and everyone who had a defensive duty did it with due diligence.
"And after that, the subs made a big difference for us."
