South Shields were caught by a sucker punch after failing to make their possession count at Billingham Synthonia.
The Mariners enjoyed most of the ball in the Ebac Northern League Division Two fixture, without being able to make clear-cut chances as they failed to score for the first time this season.
They were made to pay for that in the final seven minutes, with Julio Arca sent off for a last man foul and then Sam Garvie slotting home the only goal of the game a minute before the end to spark home celebrations.
It marked a second successive defeat in the league for Shields, who remain six points clear at the top after Ryhope CW lost 3-2 at home to Chester-le-Street Town on the same day.
In general, though, the teams chasing promotion are now more closely bunched, with seven points separating the top four.
Both sides struggled to gain any rhythm on what was an uneven surface, but Shields did have the majority of the ball from the outset.
Nevertheless, they were not able to test home goalkeeper Jack McLaren, and that was a pattern which continued throughout the 90 minutes.
The first half-chance came in the 10th minute when Ben Riding produced a good delivery from the left which David Foley was just unable to get on the end of.
Adam Sakr was the provider five minutes later when his cross from the right took a deflection before finding Warren Byrne, who fired wide of the target.
Shields were pressing, and Byrne had a shot blocked before a decent cross from John Grey almost found captain Leepaul Scroggins. It was the story of the Mariners’ day.
A menacing corner from Foley took a deflection and just evaded one of the Shields attackers, while a penalty appeal was turned down after Byrne fell in the box.
It remained one-way traffic for the rest of the half, but again McLaren was not kept busy.
After a terrific run from the left by Foley, Byrne had an effort blocked, while the hosts did excellently to cut out a through ball by Byrne just as Foley was about to run through on goal.
A similarly important intervention came soon after when Foley looked set for a shot at goal, while Byrne was played in with a minute of the half remaining by a superb Arca ball, but the offside flag was controversially raised.
The sides therefore went in at half-time with the game goalless, and Shields knew their creativity would have to improve if they were to make their possession and territorial advantage count.
However, it was Synthonia who created the first chance of the second half, with a stinging volley from the edge of the box by Matthew Osmond well palmed over by Shields goalkeeper Gareth Young.
At the other end, Scroggins sent a shot well over from 25 yards, while some mesmerising skill by Arca saw him beat his man on the right before whipping over a cross which just evaded those in the middle.
The visitors saw appeals for a penalty again waved away when Foley fell under a challenge, and Arca had a shot blocked as it looked set to be one of those days.
The Shields possession became more and more dominant at that stage, and Byrne had two efforts blocked as he looked to make the breakthrough.
However, after that spell of pressure, Synthonia came more into it as the game became more stretched.
A shot from a tight angle was well held by Young as the hosts fired a warning sign that they were still capable of taking maximum points.
With seven minutes left, they underlined that even more.
A Shields corner was twice cleared and Synthonia broke. All it took was one pass to put a home attacker through on goal, and with Arca behind him, the Mariners midfielder had little option but to sacrifice himself and take the inevitable red card for a professional foul as he pulled him back.
Shields looked like they would see the game out to take a point, but Synners snatched all three with a minute remaining. Osmond ran at the defence from the right and slipped a ball through to Garvie, who did brilliantly to take it past Shields debutant Ibby Hassan before firing low past Young.
The Mariners were unable to respond so late in the game, and were left to reflect on a second straight league loss ahead of Tuesday’s home fixture against Gateshead in the Durham Challenge Cup.
SOUTH SHIELDS: Young, Carson, Grey (Hall 81), Hassan, Riding, Arca, Sakr (Teasdale 57), Scroggins (c), Byrne, Foley, Phillips (Wightman 73). Subs not used: Pocklington, Briggs.
Sent off: Arca (83).
WORDS: Daniel Prince. IMAGE: Peter Talbot.