Darlington manager Martin Gray rested all his regulars, and fielded almost a team full of youngsters against New Mills – and they were still good enough to pick up the three points.
It was one of the first team squad who put Quakers in front on 17 minutes when Paul Weldon picked him out with a good pass, and the Frenchman ran into the box and beat New Mills emergency keeper Aaron Chalmers with a left foot shot.
But New Mills levelled a few minutes later when Brandon Windsor fired in off the bar after a good run into the box.
Quakers nearly regained the lead a few minutes before half time, when Ryu Williamson hit the post from 10 yards out.
However, the impressive opened up the New Mills defence just after half time, when Ian Watson made a great run up the left and crossed for Matty Pennal, who played at Seaham Red Star earlier in the season, to head home.
Pennal nearly got another, but his shot from the edge of the box hit the post.
Sub Lewis Walton, on for Ian Watson, made an instant impact when he got the third, with a shot from the edge of the box after the ball had been half-cleared to him.
Quakers will now prepare for a play off semi final against Spennymoor at a packed Heritage Park on Wednesday night.
Darlington: Mark Bell, David Mitchell, Paul Weldon, Jose Wilson, Matty Lovegreen, James Marley, Nelson Mota (sub Adam Lee-Shields), Daniel Wheeler-Andrews, Matty Pennal (sub Connor Briggs), Ryu Williamson, Ian Watson (sub Lewis Walton)
Subs not used:
Lewis Rees, Peter Jameson