A 9th minute goal from Barry Man of the Match, Luke Cooper, was just enough to earn Barry three points in the return festive fixture at Windmill Lane.
Travelling support made up a large amount of the 550 fans at the game, as Barry went four points clear at the top of JD Cymru South.
The early goal came from a corner on the Barry left with Cooper outjumping his marker to head home.
It was a tight match, though, and Barry had to defend doggedly in the second half, especially after the sending off of Chris Hugh for a second yellow card in the 58th minute left Town down to ten men with more than half an hour to play.
Llantwit’s numerical advantage was clear and in the final minutes, Mike Lewis’s goal led a charmed life, with one effort coming back off the inside of the post, and a number of scrambled clearances inside the box, but Barry held on.