Finding an extra gear, Macclesfield had dominated this encounter for the first 80 minutes; but then, as they have done all season, fell apart at the death.
It was the Cheshire side that came quickest out of the traps with Mathew Tipton crashing a shot into the side netting on four minutes.
Two minutes later Martin Bullock jinked past his full back, before picking out Colin Heath, whose first-time shot from eight yards was brilliantly poked wide by Carl Muggleton.
Mansfield responded when man-of-the-match Barker produced a stunning first-time shot, which was finger-tipped wide by Jonny Brain.
They got the ball in the back of the net on 29 minutes, when Kevin McIntyre met a pinpoint Tipton cross with a firm downward header that crashed off the upright. The ball rebounded to Bullock, who stroked the ball home, only to be ruled offside.
Macclesfield took the lead on 49 minutes when Heath, given only his second start of the season by Ince, repaid his faith with a spectacular 30-yard shot from the diagonal, which flew into the far corner, maybe more through luck that good judgement.
Mansfield were then unlucky not to respond when a John Mullins drive crashed off the upright.
However, they were back on level terms on 64 minutes when Brain could only palm a fierce close-range header from Barker into the path of Giles Coke, who bundled home from four yards.
Macc came back fighting and in the 80th minute skipper David Morley gleefully volleyed home from 10 yards.
However, the defence was once again suspect, as two minutes later Barker was left unmarked to head home from six yards.
Worse was to follow as Morley blatantly handled a Michael Boulding header for Barker to slot home his tenth goal of the season from the resulting spot-kick.