With the ninety minutes up and trailing a goal behind Glantraeth were harshly punished for pushing forward for an equaliser as Isa twice scored in added time to give a misleading impression of what was a closely fought game that might have swung either way.
Glan had a great chance to take the lead after only 58 seconds as a Chris Evans corner kick from the right found Emyr Rowlands unmarked at the far post but with the ball swirling in the strong wind Glan's acting manager could not get any power on his header and the ball passed harmlessly wide.
Two minutes later the Flintshire side went ahead as a long throw from the right caused problems giving Sam Hugh the space to sweep the ball into the bottom corner. Not for the first time this season Glan had conceded an early goal and were forced to chase the game.
John Leonard and Neil Wynne both went close as Isa enjoyed the better of the opening period but Glan struck back in the 19th minute. Anthony Hughes looked to be closing in on goal when a last gap tackle from Paul Connolly forced the ball for a corner. Chris Evans swung the ball in for James Burgess to meet with a header that was blocked in flight but as the ball spun loose Gareth Owen connected perfectly to send the ball powerfully past keeper Stuart McIntosh.
The goal lifted Glan who were now playing some good controlled football in difficult conditions although it was Isa who came closest to another goal on 29 minutes as Dean Handstaff struck the bar with a fine effort.
With the interval approaching the visitors were now well on top and there was growing frustration in the Isa ranks at their inability to keep the ball. Caerwyn Roberts had a shot blocked on 33 minutes then a fine move down the right opened up the home defence with James Burgess going close then Emyr Rowlands met a corner kick from Chris Evans, McIntosh diving to his left to save.
A string of corners was keeping the Isa defence occupied and as Glan continued to push forward Anthony Hughes cleverly turned his marker before firing wide and another fine passing move two minutes before the break involving Caerwyn Roberts and Mark Owens led to Anthony Hughes's centre passing across the face of goal with no-one to apply the finishing touch.
The visitors never quite carried the same threat in the second period and after Dean Handstaff had fired over Isa went ahead on 58 minutes as with Glan vainly appealing for an offside flag Barry Calder was allowed to run on unchallenged for an easy conversion.
Glan continued to play some good football but were struggling to open up the home defence. Isa had settled and were now having a measure of control with Handstaff and substitute Dan Farrell missing good opportunities to put them further ahead.
As the game entered added time Glan were desperately pushing forward when they were caught on the break in the 92nd minute. Kevin Roberts made a good tackle as the home side threatened but the ball fell nicely for Farrell to blast the ball into the roof of the net and two minutes later there was more gloom as a long ball caught Glan short at the back and Alan Dawson was able to run on and score a fourth.
With the game entering its 96th minute Mark Owens pulled a goal back for the Anglesey side, pushing the ball into an empty goal after a mistake by keeper Stuart McIntosh.