Exiles' keeper Jordan Wright was his team's saviour in a tale of two penalties at Rodney Parade.
The towering custodian frustrated his old club - superbly stopping Charles Vernam's 74th minute spot kick, this after his Mariners' counterpart Jackson Smith had brilliantly saved County raider Nathan Opoku's penalty on the hour.
Port's swash-buckling second-half display was in complete contract to their rather colourless show before the break. Though, resilience in defence and midfield sweat was a feature Christian Fuchs' men displayed throughout this encounter at NP19.
Indeed, this vital point gained, might have been three, had it not been for a five-star showing from Grimsby's borrowed Barnsley custodian Smith, the youngster thwarting County substitute Tanatswa Nyakuhwa and the excellent Ciaran Brannan, in addition to Opoku as Port roared forward seeking the crucial victory that would have taken them out of the League Two relegation places.
The Exiles, who have trickly matches away to Swindon, MK Dons and Salford clubs with promotion aspirations in the next nine days, are now only two points from safety after 22nd placed Shrewsbury crashed at Colchester, though back-makers Harrogate had a rare win, shocking Cambridge United in Yorkshire.
County fielded a back-four strategy implemented in the second half at Bristol Rovers last Saturday - and it clearly paid dividends. Tom Davies slotting in at left back to supplement centre half Matt Baker and Ryan Delaney, Lee Jenkins was ruled out through injury, experienced Liam Shephard was right-side defence.
This was a sparkling Football League bow for Austrian midfielder Sven Sprangler, signed from Scottish Championship outfit St Johnstone late in the January window, borrowed Leicester striker Opoku returned up front, supported by Ged Garner and the outstanding Michael Spellman. Utility man Cole Jarvis taken from Merthyr Town in the January window, made the bench, and later made a positive impression.
The Mariners, eying a play-off ticket, made a quartet of alteration, recalling skipper Kieran Green into central midfield, Geza Turi moved to a holding role, left-back Reece Staunton and centre back Tyrell Warren were the other adjustments to a side held 2-2 by MK Dons at Blundell Park last Saturday.
Buoyant Grimsby, who entertain Premiership strugglers Wolves in a fourth round FA Cup tie a week tomorrow [Sunday], have taken 17 from their last 21 points. They almost profited from Newport nerves in the 10th minute. Wright uncharacteristically mishandled, Vernam's resulting corner almost allowing Jaze Kabia to net at the far post.
Heavy pre-match downpours had, thankfully, given way bright sun interludes, but a plethora of robust challenges from both sides and play littered by miss-placed passes studded this grey encounter in the opening half hour.
The visitors had forced nine unproductive by the break, with County fending off set plays for their lives, but skipper Baker needed to be at his vigilant best to snuff out the menace of Andy Cook on 39 minutes.
Moments before this, Green's flicked header rattled the near post from another Vernam corner. Yet it was the Port who might have sneaked a lead in the second minute of added time. Spellman beat off Staunton at the near touchline to feed Garner who, unbalanced, screwed his 12-yard effort wide.
County, operating a high press, forced a couple of quick corners after the restart. Fuchs' battlers should have been in front on 61 minutes, of course. Mariners' defender Harvey Rodgers tripped Garner in the area, referee Declan Bourne rightfully pointing to the spot.
Yet Newport's joy was supressed as Opoku's low penalty was brilliantly saved by Grimsby's Smith, who sprang to his right to divert the kick - the gloveman then foiling County sub Nyakuhwa and Brennan later.
Yet, Port were indebted to keeper Wright on 73 minutes buzzing Kabia drew a foul from Baker in the box - Exiles' keeper then superbly stopping Vernan's resulting penalty blast.
County so nearly served maximum retribution as time ebbed away, though. Substitute Jarvis, after seizing the ball in midfield, split a retreating Grimsby rear guard with a sublime ball, Spellman's angled pass somehow evading three waiting Exiles in the area.
Newport County [4-3-3 ]
Jordan Wright
Liam Shephard
Matt Baker [C]
Ryan Delaney
Tom Davies
Cian Brennan
Sven Spranger
Harrison Biggins
Michael Spellman
Nathan Opoku
Ged Garner
Subs
Shaun MacDonald [GK]
Cameron Evans
Anthony Glennon for Garner 79 mins
Joe Thomas for Shephard 68 mins
James Crole for Opoku 88 mins
Tanatswa Nyakuhwa for Biggins 68 mins
Cole Jarvis for Sprangler 79 mins
Grimsby Town [4-1-4-1]
Jackson Smith
Harvey Rodgers
Tyrell Warren
Cameron McJanet
Reece Staunton
Geza Turi
Kieran Green [C]
Jaze Kabia
Evan Khouri
Charles Vernam
Andy Cook
Subs
Sebastian Auton
Maldini Kacurri
Jamie Walker for Khouri 81 mins
Darragh Burns for Kabia 81 mins
George McEachran for Turi 67 mins
Clarke Oduor
Tyrell Sellers-Fleming for Vernam 81 mins
Referee: Declan Bourne
Assistants: Andrew Ellis & Steven Plane
Fourth Official: Jack Clench
Attendance:3.898 [388 ]