After an excellent first half display which failed to field a goal, all that good work was undone within four minutes of the restart as the ball twice ran kindly for Scott Taylor to find the back of the Mansfield net.
But Stags' never-say-die attitude paid off in the end as Arnold beat Adolfo Baines from outside the box to earn a deserved point from the strange surroundings of the National Hockey Stadium and its concrete cows.
Martin Gritton had an early header saved and Jason White saved smartly from a Jon-Paul McGovern free kick in an even first half in which Stags kept the Dons comfortably at bay.
But Taylor broke through and Mansfield had to withstand a fearsome spell of pressure from the Dons as they looked for a killer second.
But that never materialised as Mansfield began to press hard themselves and Gritton, Jon D'Laryea and Simon Brown all came close before Arnold earned the point which was a great tonic for the Stags ahead of Saturday's visit of high-flying Wycombe.
Dons, without top scorer Izzy McLeod, rarely tested White and were left frustrated by their gutsy visitors who had something to show for their night's endeavours
With Matt Hamshaw unavailable after his bereavement, Brown returned to the Mansfield starting line up.
Stags almost stunned the home side on four minutes after a neat move down the left.
Conlon headed perfectly on to Boulding whose cross was met by a Gritton header from six yards that, unfortunately for Mansfield, was straight at keeper Baines.
Both Jelleyman and Boulding wasted good crossing opportunities when presented with acres of space down the left.
Both sides were trying to play football but the early flow was hampered by a succession of free kicks.
Andrews was well wide with a long range effort for the Dons and Stags' appeals were ignored after a D'Laryea effort struck McGovern's hand in the box.
Smith went on an exciting burst down the centre on 23 minutes which ended when he was upended by Jelleyman, the Stags defender yellow-carded for his troubles.
McGovern took just one step before curling the free kick over the Stags wall from 25 yards and White did well to get across and prevent the ball creeping inside his right hand post.
Boulding raced away down the left onto a Gritton flick but chose to shoot from a difficult angle and his low effort was easily saved.
Brown then cut in from the left only to shoot tamely at Baines with better options either side of him.
McGovern had at attempt well wide from almost 30 yards as Stags continued to defend well and frustrate the Dons.
On 37 minutes Knight headed over from a long Diallo cross from the right.
Then a poor Dawson backpass almost let in Knight and White read it well to get there first and clear.
Stags could feel pleased with their first half eforts as the sides went in goalless.
But Mansfield were rocked by a home goal within four minutes of the restart.
The Dons began the half passing well and edged ahead when Mansfield only half cleared a low McGovern cross from the right as far as the incoming Taylor whose 15-yard shot took a deflection on its way into the net.
It was his first goal in 29 games but a vital one for the Dons' promotion push.
Mansfield cleared a home corner and Buxton twice won important headers as the Stags found themselves under a spell of intense pressure for the first time on the night.
Mansfield did have a brief opportunity at the other end when slack home passing gave the ball to Gritton who made space before getting in a fine shot that Baines turned away one-handed on 54 minutes.
Diallo was booked four minutes later for his tackle from behind to fell Boulding. Dawson's free kick was eventually cleared out to D'Laryea just outside the box and his ferocious shot was not far wide of the right hand post.
On 64 minutes Billy Dearden made a double change as Rory Boulding replaced Gritton up front and Arnold came on for Michael Boulding on the left of midfield.
Buxton almost let in Knight when he gave up possession midway in the Mansfield half. But Buxton did not allow Knight to get clear and stuck with him, eventually getting in the crucial challenge as John-Baptiste got across to help.
Stirling replaced Smith for the home side on 71 minutes.
An Arnold free kick from the left was flicked on by Brown and, with the goal at his mercy, the ball flew over John Mullins' head just too high to reach.
Baldock replaced Knight for the last nine minutes as Mansfield threw everything they could at the home defence which stood solid.
As the game entered the last minute Conlon found Arnold who made space before firing in a shot which Baines was down well to save.
But in the first minute of stoppage time the lively Arnold again took possession 25 yards from goal and rifled in a low unstoppable shot that gave Baines no chance.
Dons substitute Edds blasted wide with a swerving shot with the last kick of the game which would have been cruel on the visitors.

MATCH DETAILS
DONS: Baines, Lewington, Diallo, O'Hanlon, McGovern, Mitchell, Andrews (Edds 89), Smith (Stirling 71), Knight (Baldock 81), Taylor, Butler.
Subs not used: Hayes, Harper.
STAGS: White, Mullins, Jelleyman, D'Laryea, John-Baptiste, Brown, Dawson, Buxton, Conlon, M. Boulding (Arnold 64), Gritton (R. Boulding 64).
Subs not used: Muggleton, Hjelde, Reet.

REFEREE: Grant Hegley of Hertfordshire

GOALS: Dons - Taylor 49. Stags - Arnold 90+1.
CAUTIONS: Dons - Diallo 58 (foul on M. Boulding). Stags - Jelleyman 23 (foul on Smith).

STAGS MAN OF THE MATCH: Stephen Dawson.