A late own goal by Kingsley James gave Dartford a shock away win at the Swansway on a cold Tuesday night.
Oli McBurnie opened the scoring, but James was the unfortunate man to put through his own net to decide the game after Nathan Green had leveled.
Chester dominated the first half, with John Rooney sending the first warning sign - shooting straight at Deren Ibrahim.
Craig Mahon was causing constant problems down the wings, and his first opportunity to cross found McBurnie - but the Bantams loanee stabbed wide of the post.
Matty Hughes was the next Blues player to try his luck, but Ibrahim saved again - this time from an acute angle.
Mahon linked up with McBurnie once again a matter of minutes later - but the latter's header was well saved by the keeper.
McBurnie was proving to be a real problem for Dartford, however it was without reward as he went close again with a header - this time just wide of the post.
Deren Ibrahim was then called into action again, making the best save of the lot - a one-hander to deny Mahon who hit his shot on the turn.
Nevertheless, after the break the deadlock was broken when McBurnie glanced home from a Mahon cross.
However, the lowly visitors were back level a matter of seconds later when Nathan Green chipped Worsnop.
The Darts pushed on for a winner following Green's goal - and Harry Crawford hit a shot which skimmed the bar on its way over moments later.
Steve Burr's men pushed on for a winner, but with no real cutting edge up front - Hughes striking over and Kingsley James having a shot blocked from a corner.
But, James did find the net with a minute of normal time added - but it was in the wrong net.
An inswinging 89th minute corner was sliced in at the near post by the midfielder - an unfortunate end to an unexpected defeat.
Chester: Worsnop, Higgins, Kay, Heneghan, Touray, Abbott (McConville 79), James, Rooney (Richards 79), Mahon, Hughes, McBurnie
Subs Not Used: Viscosi, Hobson, Charnock.
Dartford: Ibrahim, Richards, Driver, Dallison, McAuley, Crawford (Daley 90+1), Bradbrook, Sweeney, Noble, Harris, Green.
Subs Not Used: Burns, Collier, Hayes, Kessell
Scorers: McBurnie 54; Green 55, James (OG) 89.
Referee: Karl Evans (Wigan)