Padraig Amond proved Newport's hero again as Mansfield were denied a Sky Bet League Two play-off semi-final advantage at Rodney Parade.
Mansfield had led from the 12th minute through CJ Hamilton and looked like taking a crucial lead into Sunday's second leg at their One Call Stadium home.
But County substitute Ade Azeez was upended by Stags goalkeeper Conrad Logan seven minutes from time and Amond, who scored the FA Cup winner against Leicester from the penalty spot in January, equalised to make it 1-1.
It was success at the second attempt as Logan pushed out Amond's spot-kick, the Irishman first to the rebound to score his 23rd goal of the season.
Newport had squeezed into the play-offs when Jamille Matt levelled three minutes from time in the final game at Morecambe on Saturday.
But momentum was on County's side with six wins in a 10-game unbeaten run.
Mansfield might have been forgiven for feeling downbeat after missing out on an automatic-promotion spot with MK Dons claiming the weekend's winner-takes-all prize.
But the Stags started on the front foot and Newport could have been reduced to 10 men after five minutes.
Mark O'Brien stopped the pacy Tyler Walker's turbo-charged burst towards goal, but Charles Breakspear controversially brandished a yellow card when many referees might have shown red.
Mansfield dismay, however, turned to delight within seven minutes.
Jacob Mellis seized on a turnover in possession to free Hamilton down the left of the penalty area, and the winger unleashed a ferocious drive high into the net for his 14th goal of the season.
Mellis, the best player in the opening half-hour, drove over as Mansfield continued to win a midfield skirmish conducted at breakneck speed.
Newport had toiled to find any fluency until Mickey Demetriou flicked on Matty Dolan's free-kick.
Matt arrived with a far-post header but Logan superbly scooped the ball away at point-blank range.
That was the signal for County to apply pressure and battle for headers and second balls in the Mansfield box.
But it was the Stags who should have been further ahead at the start of the second half when Walker broke free and rounded County goalkeeper Joe Day.
Walker was off-balance though as he took the shot and Demetriou was able to clear his trickling effort.
Newport almost equalised within seconds when Amond reached Matt's header and forced Logan into a sprawling save at his near post.
Walker's pace was a constant problem for the Newport defence and County were grateful that he failed to fully connect with a volley which Day fell on comfortably.
County sent on Azeez to form a muscular strike partnership with Matt and, after Robbie Willmott saw his offside effort ruled out, the ploy worked as Amond struck at the second time of asking.
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