A Guiseley penalty 12 minutes from the end condemned South Shields to their fourth league defeat of the season on Saturday.
In treacherous conditions in West Yorkshire, an even game looked to be headed for a 0-0 draw until the lively Lewis Whitham converted from the spot for the hosts.
The result meant Shields missed out on the chance to extend their lead at the top of the Pitching In Northern Premier League, which now stands at three points.
The Mariners were unchanged from the team which beat Marine 2-1 a week earlier and they started in positive fashion, with Darius Osei shooting wide from the edge of the box in their first opening.
This was a meeting of the league's two most in-form sides, and Guiseley demonstrated their ability with a series of half-chances, the best of which saw Jake Cassidy flick the ball wide after a low cross from the right.
At the other end, goalkeeper Cameron Mason was twice called on to make sharp saves at his near post.
The first of them came when Martin Smith's strike from distance was deflected to Osei and he fired goalwards from the edge of the box, before Mason also denied Mackenzie Heaney with a sprawling stop.
Clear-cut opportunities were difficult to come by in changeable conditions, with rain regularly teeming down and adding extra zip to the surface.
A tight first half was arguably edged by Shields, but the second half was a scrappier affair.
Tom Broadbent stabbed an effort which was well-cleared in front of goal and Smith dragged a shot wide from the halfway line after a loose clearance from Mason.
But it was Guiseley who went closest to taking the lead on the hour mark when Callum Chippendale's sweet strike was brilliantly cleared off the line by the head of Robert Briggs.
Whitham was consistently Guiseley's biggest threat and he forced Boney into a low save with a strike from distance before being at the heart of the decisive moment as he was tripped in the box.
He stepped up to slide the penalty into the bottom corner and provide his team with a lead they would not relinquish.
Shields pushed for an equaliser but were unable to find a way past Mason in the Guiseley goal.
He held onto an attempt from distance by Smith and twice watched on as excellent crosses from substitute Dylan Mottley-Henry and Smith begged a conversion, but narrowly missed a decisive touch.
Guiseley saw it out to claim the points, with the Mariners set to have a chance to bounce back on Tuesday when they travel to Matlock Town.
South Shields: Boney, Hunter, Broadbent, Liddle, Morse, Smith, Mongoy, Briggs, Osei (Mottley-Henry 62), Heaney (Alessandra 72), Adams (c). Subs not used: Doherty, Gomes, Dobson.
Attendance: 953.
Image: Kev Wilson.