Chesterfield substitute Will Grigg struck twice late on to seal a 3-0 win at Newport after Dilan Markanday had been gifted a first-minute goal.
The visitors took the lead after just 43 seconds as a mix-up between Exiles goalkeeper Nick Townsend and centre-back Kyle Jameson allowed Markanday to roll the ball into an empty net.
Grigg then climbed off the bench to net a double as Chesterfield, who had drawn their previous three matches 2-2, claimed a three-point haul that moves them up to seventh in League Two.
After a low-quality first half, County pushed hard for an equaliser in the second half, with substitute Kyle Hudlin poking one shot wide at the far post and then hitting the post with a chipped cross-shot.
Chesterfield goalkeeper Max Thompson also almost stumbled over the line after crashing into the post as he caught a corner.
But it was another substitute, Grigg, who had the final say with two quickfire goals on the break.
The former Northern Ireland international slid in to make it 2-0 with five minutes left on the clock and added a third two minutes later with a neat finish.