It looked promising for United after they took a 15th minute lead through Steve Butler. Gary Crawshaw forced his way to the byeline and passed inside to Butler who made no mistake from close range.
But on 24 minutes Enfield levelled; former Ducks and Watford veteran Steve Terry heading a far post corner powerfully past Simon Brown.
United, without the injured Jermain Darlington, left much of their approach work to Darlo's fellow wing-back Kieran Gallagher. Indeed Gallagher was unlucky as the first half drew to a close with a couple of long range efforts, and just before the break another Gallagher screamer hit the upright with keeper Andy Hall beaten.
With so much at stake, the second half failed to live up to expectations and neither keeper had a lot to do. Butler headed a Crawshaw cross just over (64 minutes), and Hall saved well from Mike Bignall (82 minutes).
With United pushing up in search of a late winner, just as they had done three days earlier against Basingstoke, the visiting E's broke with telling effect three minutes from time.
Mark Bentley burst through unchallenged and, despite Brown getting a hand to Bentley's shot, Steve Darlington followed up to slide the ball in. Cruel luck on United who deserved at least a point.