Two goals up at the break after a dominant first half display Glantraeth looked to be heading for a second successive victory but a quite remarkable turnaround in the second period saw bottom club Llandyrnog United eventually run out comfortable winners.
There was no sign of what was to come as Glan took the game to the visitors from the off with Anthony Hughes, James Burgess and Gareth Owen all narrowly off target in the opening fifteen minutes.
The home side took a deserved lead on 26 minutes a good move involving Adam Jones, Emyr Rowland and James Burgess ended with a cool finish from Anthony Hughes.
It was all Glantraeth and more good link up play between Chris Evans and Kevin Roberts gave Burgess the chance of a left foot shot that was deflected for a corner. Dyrnog half cleared the ball as it came over giving Adam Jones a shooting opportunity from 25 yards that went wide.
Keeper Arwel Hughes had to go full length to save from Kevin Roberts on 31 minutes then Chris Evans had an effort deflected wide before Glan finally went two up three minutes later, Gareth Owen heading home as Caerwyn Roberts swung in a cross from the right.
Stung into action the visitors threatened with a quick break bringing a great saving tackle from Danny Wade then Sion Roberts headed wide when in a good position.
The half ended with Glan back on the attack, keeper Hughes saving well from Anthony Hughes and Burgess hitting a tremendous shot on the turn that was blocked in flight.
It had been an impressive first half display by Glantraeth and they came out after the break to brilliant sunshine which played a part in the visitors pulling a goal back on 47 minutes, Gareth Owen losing the flight of the ball in the air and giving Danny Jones an easy chance to score.
The game was now much more evenly fought and things took a bigger turn for the worse for Glan on 67 minutes as an overhead effort from Anthony Marshall was saved by Marc Newbould only for the ball to fall for Tom Sharples to score with an easy tap in.
It too a great tackle from Gareth Owen three minutes later to prevent substitute Endaf Jones putting the visitors ahead then Owen was in action at the other end as only a point blank save from Hughes prevented him putting Glan back in the lead.
Llandyrnog were now looking the more likely winners as Eppy McFadden and Adam Jones both had to make tremendous clearing headers in the space of two minutes but it was a brief respite as Sharples got his second on 77 minutes, heading home from an in-swinging corner from Roger Beech.
With five minutes remaining David Alan Jones brought a full length save from keeper Arwel Hughes but with Glan desperately trying to rescue the game they were caught out on 87 minutes when Sion Roberts scored at the second attempt and two minutes later the same player put Dyrnog 5-2 ahead.
In the final minute Alan Jones pulled a goal back for Glantraeth cutting in from the right and finishing with a left foot shot that gave Hughes no chance.
The faces of the Glantraeth players at the final whistle told their own story as an afternoon that had started off so promisingly had ended in defeat with the Anglesey side now only two points of the bottom of the table.
Glantraeth: Marc Newbould, Eppy McFadden, Adam Jones, Danny Wade, Gareth Owen, Caerwyn Roberts, Anthony Hughes, Emyr Rowlands, James Burgess, Kevin Roberts, Chris Evans (David Alan Jones 67).