A third win in four starts for Caernarfon was sealed by first half goals from Osian Evans and Zack Clarke.
For Cymru Premier newcomers Trefelin, it was a fourth straight loss for a team currently propping up the table.
The deadlock was broken after just eight minutes at The Elsey Creative Ynys Park Stadium, Clarke seeing his fierce drive blocked before Evans drilled home a low finish from 15 yards.
Town’s lead was doubled with 36 gone when Evans’ deep cross from the left to the back post was volleyed goalwards by Adrian Cieslewicz and although keeper Scott Coughlin kept the ball out, Clarke was following up to head home.
Trefelin were unlucky not to pull one back after the break when Daniel John won the ball in a swift counter attack, but his effort rebounded off the bar to safety.
Caernarfon also rattled the goal frame before in added time Trefelin captain Jordan Davies was red-carded for a late challenge after a monitor check by referee David Morgan.
Adam Davies condemned his former club to defeat when he headed in the only goal of the game at The Blue Turtle Arena.
A crowd of 1,068 watched the Seagulls take on the Wingmakers in a battle of past Cymru North champions.
Airbus should have taken the lead when Bay got caught napping at the back, but keeper Mark Halstead was quick off his line to deny George Peers.
Nathan Peate blasted over from a great position for the hosts before Dan Roberts headed wide from point blank range following a Josh Williams corner.
Peers had another golden opportunity when an Evans cross from the left arrived at his feet as he turned, but again Halstead was able to block.
The all-important goal arrived on 39 minutes when Sam Hart lofted a high ball into the box from the left and Davies headed past Louis Fallon to score.
Davies also had a shot kicked off the line before the break.
In the second half, the lively Kaiden Cooke regularly tested the Bay defence, one shot forcing a good low save from Halstead.
Roberts almost made it 2-0 at the other end when his deflected strike dipped inches over the bar.
An own goal from Jack Thorn in first half injury time was enough to bank maximum points for Briton Ferry Llansawel.
Despite taking a 16th minute lead through Caio Davies, Holywell slumped to a fourth loss in a row.
Elliott Dugan levelled on 31 to make it all-square at half time.
Holywell’s Owen Davies missed a penalty just before the hour, and the hosts paid the price when Owen Brain put Barry 2-1 up after 72.
Jack Shaw sealed an away success for the new leaders with a third goal five minutes past the 90.
A first defeat for Llandudno after three consecutive wins – but they were unfortunate not to get a point at Penybont.
The hosts took a 43rd minute lead when a Ryan Hill corner was played to Owen Pritchard whose shot ricocheted up into the air and Tom Mehew made it 1-0 with an acrobatic finish.
Four minutes into the second half, Rhys Griffiths’ side scored a controversial second goal.
Following another Hill corner, a clear foul on a Llandudno player went unpunished before Mehew volleyed in his second.
Tudno fought hard to get back into the contest and only a last-ditch tackle denied Cammron Morris a goal after keeper Daniel Higgs had kept out an Adam Stephens shot.
Higgs frustrated the Seasiders again with a fine save from an Adam Stephens overhead kick.
Kieran Lloyd lashed over from a good position and Morris was again thwarted by Higgs when a goal looked certain.
Penybont’s Noah Daley got it all wrong when presented with a sitter at the ither end.
Llandudno finally pulled one back in the 90th minute when a free kick was played short to Kieran Smith, whose side-footer rolled past a static Higgs, but it was too little, too late.
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