Updated: Apr 2
A stoppage time free-kick from Fin Sinclair-Smith condemned South Shields to a 2-1 defeat at Bamber Bridge on Saturday.
The Mariners looked set to return to South Tyneside with a point after Dylan Mottley-Henry cancelled out Paul Dawson's opener just seconds after being brought on.
Bamber Bridge were reduced to 10 men when Nathan Pond was given his marching orders but they struck the decisive blow in the dying stages as Sinclair-Smith found the top corner.
The Mariners' advantage at the top of the Pitching In Northern Premier League now stands at nine points from Bamber Bridge, who have a game in hand.
Shields came out of the blocks quickly and had the first effort on goal as some bright play found Darius Osei and he controlled the ball well before his left foot strike was saved by Brig goalkeeper Felix Goddard.
Lewis Alessandra was brought into the Mariners' line-up and he was the next to have a sighter. His shot was blocked, as was the follow-up from Jordy Mongoy.
Bamber Bridge came into this match in fine form, and they demonstrated some of their quality as they worked the ball patiently through to Dawson and he fired into the side netting from the right of the area.
Much of the early enterprising play came from the visitors, though, and both Osei and Josh Doherty thrashed efforts over from similar positions on the left after eye-catching attacks.
They were caught out by a short corner routine at the other end as Brig took the lead on 13 minutes.
Rowan Roache slid in the delivery from the right and Dawson sent it into the bottom corner as the Mariners' bright start was punctured.
Bamber Bridge could have doubled their lead from another set-piece, but Pond's header from a Roache free-kick was straight at Myles Boney.
The hosts were bolstered by their goal and continued to pressurise Shields. Luke Mariette forced an error from Boney as the goalkeeper slipped, but the Shields man recovered well to make a well-timed tackle and clear the danger.
The Mariners were desperately unfortunate not to level the scores midway through the first half when Mackenzie Heaney picked out Robert Briggs and he hit the post from 12 yards. The ball then broke to Mongoy, whose powerful strike was kept out by Goddard before last-ditch blocks denied Osei and Briggs.
Shields also took the opportunity to try their luck from longer range on several occasions, one of which was a terrific attempt from Heaney which Goddard tipped over.
Bamber Bridge took their lead into half-time and Shields continued to be frustrated in the opening minutes of the second half.
Kevin Phillips opted to bring Mottley-Henry on just after the hour mark and the substitute had an instant impact as he equalised with his first touch.
The Mariners had worked the opening patiently with play down the right of the area between Jordan Hunter and Alessandra, who pulled the ball across for Mottley-Henry to finish first-time from close range.
The home side were reduced to 10 men shortly afterwards as Pond was punished for a dangerous lunge on Doherty midway inside the Bamber Bridge half.
Doherty was in the thick of the action and he was the first to threaten a goal after the sending off as his strike from distance whistled past the post.
Brig's threat going forward was not completely nullified by this stage, and they almost went back in front with a sweet shot from Luke Mariette which narrowly cleared the crossbar.
Harry Gardiner was introduced for his Shields debut 10 minutes from the end and he too almost had a dream start, but his glancing header from a Hunter cross went wide.
The Mariners pressed for a winner but were hit with a sucker punch at the other end three minutes into stoppage time as Sinclair-Smith's superb free=kick found the top corner.
Shields will aim to bounce back next Saturday when they host Nantwich Town.
South Shields: Boney, Hunter, Doherty, Liddle, Broadbent, Smith, Heaney, Briggs (c), Osei (Mottley-Henry 62), Alessandra (Gomes 83), Mongoy (Gardiner 80). Subs not used: Shokunbi, Morse.
Goal: Mottley-Henry (63).
Image: Kev Wilson.