Jason Kennedy's early strike set Darlington on their way to a win against Peterborough and a play-off semi-final clash with Rochdale.
Ricky Ravenhill set up Kennedy to score from close range in the third minute.
Posh were then repeatedly denied by sub keeper Przemyslaw Kazimierczak, who came on for the injured David Stockdale after only 12 minutes.
The Quakers made it 2-0 in the 52nd minute when Craig Nelthorpe played in Michael Cummins to score from 12 yards.
Peterborough: Lewis, Newton (Potter 69), Morgan, Westwood, Williams, Whelpdale (Lee 49), Hyde, Keates, Boyd, Mclean (Rendell 60), Mackail-Smith.
Subs Not Used: McKeown, Charnock.
Booked: Morgan, Hyde, Boyd.
Darlington: Stockdale (Kazimierczak 12), Wiseman, White, Miller, Purdie, Wainwright, Keltie, Kennedy, Ravenhill (Main 83), Nelthorpe, Cummins.
Subs Not Used: Foster, Wright, Burgess.
Booked: Ravenhill, Kennedy, Miller, Keltie.
Goals: Kennedy 3, Cummins 52.
Att: 10,400
Ref: Steve Bratt (W Midlands).
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