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."