Shields had to battle their way to victory on a bitterly cold, blustery evening at Mariners Park.
First half strikes from Lee Mason and Robert Briggs ultimately proved to be enough, despite substitute Nathan Brown pulling a goal back for Marine in the second half.
Both sides ended the game with 10 men after Shields' Ben Harmison and Marine's Will Dunne were sent off following an off-the-ball incident.
Shields were looking to end a rare run of three home matches without a win as they aimed to take advantage of their game in hand on top two Farsley Celtic and Warrington Town.
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They were almost caught out after just four minutes, though, when a free-kick from deep by Charley Edge was caught by the wind before Liam Connell was forced to tip the ball onto his crossbar.
The Mariners gradually took control and opened the scoring in the seventh minute.
Mason and Blair Adams exchanged passes on the left before Mason impressively worked the ball onto his left foot and buried it into the bottom corner.
That was the cue for a flurry of Shields attacks as they set about making their lead more comfortable.
Phil Turnbull went close to making it two when he met a Briggs short corner and saw an effort deflected not far wide.
Marine goalkeeper Joe Hilton kept out Harmison's header from the resulting corner and also later denied Adams after he fired goalwards from long range.
The second goal arrived in the 33rd minute as Turnbull found Briggs on the right of the area and a deflection took his shot out of the reach of Hilton as it nestled in the opposite corner.
A thunderbolt from Mason narrowly cleared the crossbar as the game ticked towards half-time, while Briggs was denied his second by a good stop from Hilton.
Chances were harder to come by in the second half as the conditions took a firm grip of the match, but Shields were fired a warning when Connell was called upon to save from James Murray.
The Shields goalkeeper was beaten soon after as Brown let fly from distance and halved the deficit.
That blow may have led to some nerves for the promotion-chasing hosts, but the best chances of the latter stages fell to them.
The closest the Mariners came to extending their advantage was when a Briggs free-kick was nodded across the area by Dillon Morse to Harmison, whose header was well saved by Hilton.
Marine almost got back on level terms when Brown hit a rasping effort not far wide, before Harmison and Dunne were both sent off for an incident near the corner flag.
Shields saw the game out to claim maximum points and they will hope to build on the result when they travel to Workington on Saturday.
SOUTH SHIELDS: Connell, Baxter, Adams, Shaw (c), Morse, Turnbull, Foley (Bell 69), Briggs, Harmison, Daly, Mason (Lough 84). Subs not used: Mouanda, Lowe, Gillies.
Goals: Mason (7), Briggs (33).
Sent off: Harmison (89).