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Dartford had to settle for a point after Grimsby scored late to snatch a draw at Princes Park.
Tom Bradbrook headed the Darts in front on 60 minutes but the home side were reduced to 10 men when Nathan Collier was sent-off for giving away a penalty which Lenell John-Lewis scored with seven minutes remaining.
But despite conceding late, this was a point gained for Tony Burman's men, who defended like lions in the face of serious Grimsby pressure in the second half.
Dartford's starting line-up bore just one change from the 2-2 draw at Welling in midweek, with Max Cornhill replacing Luke Daley in midfield.
Cornhill lined alongside Peter Sweeney as part of a 3-5-2 formation. Collier dropped into the back-three with Rory McAuley and Mat Mitchel-King, with Lee Burns and Tom Bender operating as wing-backs and Elliot Bradbrook pushed forward in support of strikers Danny Harris and Tom Bradbrook.
Ross Hannah had two early efforts for the visitors. His first was a free-kick which drifted harmlessly wide but the second, an outrageous volley from 35 yards out, had goalkeeper Jason Brown beaten as it kissed the post and flashed behind.
The home side were forced into a reshuffle midway through the first half when Burns was caught late by Carl Magnay as both players slid in to win a loose ball. Magnay's foot went into Burns' chest and although he tried to continue, he couldn't - having only just recovered from a rib injury.
Ryan Hayes came on for Burns and the Darts switched to a 4-3-1-2 shape.
The hosts had been quiet going forward but they went close twice in as many minutes. Cornhill headed over from Sweeney's left-wing cross and when Grimsby failed to clear a Hayes corner from the left, Elliot Bradbrook rattled the crossbar with a strike from 12 yards.
Paddy McLaughlin got free in the Dartford box just before half-time but, under pressure from Mitchel-King, he lashed his shot over.
The first half had been a tight affair and things continued in a similar vein after the restart.
Grimsby were becoming increasingly frustrated and then, on the hour, they fell behind.
Hayes swung over a terrific deep cross from the right and Tom Bradbrook's excellent downward header found the net despite Town's desperate attempts to clear on the line.
That assist was Hayes at his best, but he lost his head moments later. Magnay was shielding the ball behind for a goal kick when Hayes kicked out at him in the corner - and was perhaps lucky to only be shown a yellow card.
Then a left-wing cross from Bender was headed straight at Mariners keeper James McKeown by Tom Bradbrook before white shirts converged to charge down a John-Lewis effort at the other end.
The pressure began to mount on the Dartford goal and John-Lewis drilled a volley over the bar after substitute Scott Neilson had touched the ball into his path. Bender cleared another effort off the line and Aristote Nsiala smashed the rebound into the travelling fans.
Neilson got in behind the home defence and the ball ran for Rhys Oates, another substitute, but he couldn't hit the target and the Darts survived again.
But they couldn't hold out much longer. A poor clearance let John-Lewis race into the box and when Collier brought him down, referee Chris Powell pulled out the red card. John-Lewis took the penalty himself, firing the ball into the top corner as Brown dived the wrong way.
Now the visitors sensed the game was there to be won and Neilson dragged a shot wide with his left foot.
A swirling cross from Daniel Parslow had Brown squinting into the sun and he did well to claw the ball out from under his crossbar.
Brown again came to Dartford's rescue in stoppage-time, saving Craig Disley's header just as the Town skipper thought he'd headed home the winner from Scott Brown's deep cross.
Dartford: Brown, McAuley, Mitchel-King, Collier, Burns (Hayes 21mins, Pugh 85mins), Cornhill, Sweeney, E Bradbrook, Bender, Harris (Daley 73mins), T Bradbrook. Subs not used: Crawford, Ibrahim.
Grimsby: McKeown, Brown, Pearson, Magnay, Mackreth (Neilson 62mins), Disley, Hannah (Oates 77mins), John-Lewis, Parslow, Nsiala, McLaughlin. Subs not used: Bignot, Clay, Walker.
Attendance: 1,285.