Dartford claimed victory at Grimsby to end the Mariners' 10-game unbeaten run.
Grimsby bossed the opening stages, and could have gone ahead had a Nathan Pond header found the target from Joe Colbeck's free-kick.
However it was the Darts who broke the deadlock when Tom Champion fired home from the right-side of the area.
The hosts pressed for an equaliser, but Adam Birchall finished clinically following a superb solo run to secure the win for the visitors.
VIEWS FROM THE DRESSING ROOM
Grimsby Town joint-manager told BBC Radio Humberside:
"It was poor from start to finish.
"We can always stand by players that have bad games, but all of them were off and not one of them can come away with any credit.
"We were putting our foot through the ball, scuffing things, we were heading it up in the air.
"There was no communication and it was just all over the place at times, which is disappointing, because of how well we have been playing."
Dartford manager Tony Burman told BBC Radio Kent:
"I am very, very pleased, the boys played excellently. It's a tough place to come, they're on a great run, they're well organised.
"We took the game to Grimsby. When we scored it gave us the belief to win the game. Our play and our support was excellent.
"We know what we're supposed to be doing. We feel people are not giving us any chance. It's a bit disrespectful, we deserve to be where we are."