It had been a fairly even first half with chances at either end – perhaps FC United coming the closest when Jordan Fagbola`s effort had to be cleared off the line by Liam Marrs.
But the hosts found themselves a man down seconds before half-time when Kevin Burgess was shown a straight red card for a challenge on Scott Kay deemed reckless by the referee.
However, the Quakers` boss Martin Gray acted positively, keeping two strikers on the pitch after going down to ten-men, and 7 minutes into the second half, that paid off when one of those, Nathan Cartman (pictured), volleyed past Lloyd Allinson in the FC united goal.
Numbers on the pitch were evened-up just past the hour-mark when Matty Hughes was dismissed for a second booking when bringing down Joe Wheatley in the area, but Terry Galbraith saw his spot-kick saved by Allinson.
Then on 77 minutes, Darlington doubled their lead when David Ferguson picked up the ball 35 yards out, ran past a couple of defenders before slotting the ball underneath Allinson.
The visitors were reduced to nine-men with 5 minutes remaining when Mike Connor received his second booking.
And a couple of minutes later, Wheatley got on the end of a Ferguson cross to make it 3-0 from close range.