It extended the fabulous unbeaten start to the season to 17 games as they saw off former Stags boss Graham Coughlan's injury-hit Exiles in relative comfort.
Keillor-Dunn gave Stags a fourth minute lead as they dominated the first half and should have gone in with more goals to their name, Rhys Oates also having a 31st minute penalty saved.
The visitors were improved in the second half.
But Keillor-Dunn did double his and Mansfield's tally on 51 minutes and that proved enough to take the points.
Baily Cargill replaced the suspended Calum Macdonald in the only change to the Stags' side and injured pair Lucas Akins and Stephen Quinn returned to the bench.
The injury-hit visitors were only able to name six players on their bench, two being Academy players Alfie Young and Nelson Sanca.
Their only change to the starting XI saw Omar Bogle coming in for Olly Thomas.
Newport produced the first attack of the game in the second minute as the ball was worked to Bogle who hurried a 16 yard finish well over the crossbar.
The visitors were looking ambitious, but Stags rocked them with a fourth minute goal.
The defence failed to properly clear an Oates cross from the right and the ball ran loose in the box, Keillor-Dunn quickly latching into it and stroking home low from 12 yards, taking him into double figures for the season.
Flint got in the way of an Evans shot on eight minutes to concede the game's first corner, which was cleared.
Oates had a fleeting chance from a free kick on 13 minutes with a shot on the turn but didn't catch hold of the ball well and it trickled to the keeper.
Then a superb forward ball from Brunt on 17 minutes was well controlled in the box by Keillor-Dunn, who forced Townsend into a save.
Stags then enjoyed a lengthy spell of possession with the Exiles holding their shape well under the intense pressure.
But the home team should have doubled their lead on 31 minutes.
Oates burst past Bennett on the left by-line and was then shoved over by his opponent.
Oates stepped up to take the penalty but he tried to place it low and central and Townsend was able to make a comfortable save.
A shove by Bogle on Brunt on 33 minutes saw him booked after already being warned for a string of fouls.
A minute later Newport boss Coughlan was also cautioned for dissent.
Good work from Bowery opened up a sight of goal for Maris, but his finish was wild and well over.
Soon after Lewis found Keillor-Dunn, whose low finish was wide of the far post.
In the first of two added minutes Johnson's cros from the right clipped the top of the bar and went over as Stags went in with just the one goal to show for their dominance.
Newport almost caught Mansfield cold in the opening minute of the second half as a neat flick from Wood saw Evans fire a low shot at goal that Pym saved.
Stags were forced to endure a few uncomfortable moment from a side that had clearly come out intending to go up a gear.
But they finally got the ball under their control and Oates sent a tempting low ball across the face of goal with Bowery inches away from touching it home.
On 51 minutes Keillor-Dunn burst down the middle and laid the ball off to Lewis, who forced Townsend to save low to his right.
But Keillor-Dunn doubled Mansfield's lead within seconds as Maris picked him out with a sublime pass down the middle and Keillor-Dunn sidefooted oast a rooted Townsend from 10 yards.
Keillor-Dunn floated another teasing ball over the keeper and across the open goal with no one capitalising.
The visitors then forced two corners in reply, the second of which saw a scramble and a shot charged down, but the home goal remained intact.
Pym was again tested on the hour as Bogle set up Evans. But his fierce finish was straight at the keeper.
Morris was booked for clattering into Lewis on 61 minutes.
Another cutting Maris pass set Oates loose on the right and his low cross again was inches away from the incoming Bowery.
More Newport pressure saw Brunt superbly block a close range shor from Wood.
Then Cargill headed straight at Townsend from a corner on 74 minutes.
Immediately Akins, wearing a protective face mask, replaced Oates up front. He was quickly into the action sending a tame shot on the turn at Townsend after a swift Stags break.
Quinn, to huge appluase, and Boateng took over from Lewis and Maris on 80 minutes and a minute later a high boot from Clarke on Akins earned him a yellow card.
Boateng was just wide with a low 18-yard shot from a half-clearance on 83 minutes.
Desperate Newport won three more corners in a row to no avail while at the other end Townsend beat away a Keillor-Dunn snapshot as he looked for his hat-trick.
STAGS: Pym, Johnson, Flint, Brunt, Cargill, Reed, Lewis ( Quinn 80) Maris (Boateng 80), Keillor-Dunn (Swan 89), Oates (Akins 74), Bowery (Gale 89). SUBS NOT USED: Flinders, Williams.
NEWPORT: Townsend, Payne, Delaney, McLoughlin, Bondswell (Clarke 55), Waite, Morris, Bennett, Wood (Palmer-Houlden 50), Bogie, Evans. SUBS NOT USED: Maxted, Thomas, Young, Sanca.
REFEREE: Thomas Kirk.
ATTENDANCE: 6,877 (223 away).