Two late goals condemned Dereham to their third defeat after a tough week.
With four games remaining and a gap of 11 points between the Magpies, in eighth, and the sixth and final play-off position, the end-of-season shoot-out is all but a dream.
It could have been different: Dereham almost opened the scoring in the second minute when Ashley Jarvis' header was cleared off the line from Danny Beaumont's corner.
After a delay for Haringey's Andre McCollin to be stretchered off, play was even with little between the sides. The visitors created a chance on the left culminating in Lauren Luke side-footing over when well-placed.
The Magpies also came close when Rhys Logan hit a 30-yard diagonal drive just off target in the 23rd minute. Minutes later the wide man gained possession inside his own half and picked out Jarvis with a fine long pass, but the striker guided the ball wide of the far post.
Play was equally competitive after the break with defences on top. In the 56th minute Haringey's Ralston Gabriel fired over from 20 yards and at the other end Sam Borrer's curler drifted off target.
Haringey missed a good chance with Anthony McDonald firing over from close range after Gabriel's knock down in the 63rd minute and they then should have taken the lead when Gabriel was put through but lifted the ball over keeper Elliot Pride and the bar.
It was a lack of concentration in the home defence following treatment to the visiting keeper, enabledthe ball to be flicked onto Chinedu McKenzie who netted from close range in the 87th minute and right on time Jordan Edwards scored a second to seal victory and rub salt into Dereham's wounds.
Dereham: Pride, Castellan, Anema (Ebbage 45), Hinton, Howell, Linford, Logan, Borrer, Jarvis, Forshaw, Beaumont (Wengzik 79).
Subs not used: Crisp, Exley, Cox.
Haringey: Paketet, Olufemi, O'Donoghue, Djassi-Sambu, Mitchell, Kirby, Luke (McKenzie 75), Richards, Gabriel, McCollin (Edwards 7), McDonald (Asamoah 75). Subs not used: Stone, Byfield.
Ref: J Crofts. Att: 129
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