Karl Ledsham struck an injury-time equaliser to boost struggling Southport and deny promotion-chasing Dartford.
Elliot Bradbrook put the hosts ahead with a fine strike from the edge of the area, before Steve Akrigg headed in Ledsham's free-kick to bring Southport level soon after.
Bradbrook then restored the advantage from the penalty spot after Ryan Hayes was brought down by Chris Lever.
But Ledsham fired home in stoppage time to give Southport a point.
VIEW FROM THE DRESSING ROOM
Dartford manager Tony Burman told BBC Radio Kent:
"I didn't think we performed as well as we should do but to be fair to Southport they kept going.
"We had too many players below par today and that cost us in the end.
"That's the first time we looked jaded.
"It's a poor goal we conceded from our point of view. We were in the lead and in control but the next goal was always going to be important and we didn't have enough in us to get it."
Dartford 12 Bettinelli 02 Rose 04 Champion 06 Bonner 16 Arber 10 Bradbrook 14 Noble Booked (Collier - 88' ) 20 Burns 07 Hayes (Wallis - 84' ) 09 Erskine (Rogers - 88' ) 11 Harris Substitutes 01 Wells 03 Green 13 Rogers 08 Wallis 15 Collier Southport 01 McMillan 02 Smith 03 Lever Booked 04 Akrigg (Lynch - 90' ) 06 Grand Booked 07 Whalley 08 Ledsham 16 Moogan 22 Poku (Chalmers - 78' ) 11 Almond 18 Tames (Stephenson - 78' ) Substitutes 13 Hibbert 17 Lynch 12 Benjamin 15 Chalmers 21 Stephenson