Cowbridge are top of the Cardiff South 1 League following a 17-14 win over Barry at the Reservoir Field.
Both teams set out with aspirations of finishing top of the league at Christmas - but with one of Cowbridge's props pulling up during the warm-up, the visitors opted for uncontested scrums before kick off.
With Barry playing down the slope in the first half, they pushed for an early scoreline but were repelled a few times by a well organised Cowbridge defence.
However, following a penalty for back chat, Barry fly-half Cam Hughes was able to push his forwards deep into the Cowbridge 22 and a well set up lineout drive saw the home pack get over the line with hooker and captain Rhys Berhens the last man up with the ball.
Hughes added the extras for what turned out to be the only try of the first half.
Barry's defence had been outstanding - but after the break, it was suddenly guilty of a few missed tackles which allowed Cowbridge through to draw level.
The hosts struck back through a well-executed backs move with full-back Austin Cafferey rounding off a slick handling moving, again converted from the touchline by Hughes, to take a 14-7 lead.
Barry opted for the posts from another penalty to take them two scores clear, but agonisingly, the ball came back off the post allowing Cowbridge to clear down the field. The lead was cut to two points but the conversion also struck the post with ten minutes left.
Cowbridge remained camped on the Barry line in the final stages, but heroic defence kept them out time and again, typified by man-of-the-match Morgan Beasley.
But with less than a minute to go, a clearing kick was charged down and a favourable bounce allowed the Cowbridge second row to pounce and clinch a dramatic derby victory.
Barry head coach Peter O'Sulllivan said: "We were frustrated before the game with uncontested scrums going against us again, as has happened numerous times this season."
"The players were gutted after the game to lose in that fashion, but they can be genuinely proud of the effort that they all put in. Both sides gave everything and the result could have gone either way."
Cowbridge have now completed their league campaign with Barry travelling to Llantwit Fardre in their final game next Saturday.
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