Admiral League leaders Penarth slipped to a 25-13 defeat at home to Abercwmboi in Division One East Central.
The Bears remain three points clear at the top of the table, despite putting in an unusually tentative performance, especially in open play.
Rhys Mottram took the lead from an early penalty only for the visitors, who won at Barry a week ago, to take advantage of a yellow card for the Bears to score the first of three away tries.
Abercwmboi had opened up a 12-3 lead by the time Mottram converted a second penalty only for the Village to score one of their own soon afterwards.
In the closing minutes, Spencer Robinson was narrowly denied from going over the line before the ball was passed to Harry Williams, who sidestepped a defender before crashing over for the Seasiders' only try of the day.
Mottram added the extras to cut the gap to two points, but in the time left, Abercwmboi raced further ahead with a penalty and a further try to round off a rare off-day at the Athletic Ground.
Penarth turn their attention to the WRU Division One Cup next Saturday when they visit Aberavon Green Stars in the quarter finals.
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Elsewhere around the Vale, Cowbridge fell to a 31-17 defeat at CR Cymry Caerdydd in Division Two - in a rehearsal for next Saturday's Division Two Cup quarter final.
Dinas Powys went down 31-7 at Penygraig in Division Three while Llantwit Major's home game with Gilfach Goch was postponed.
Old Penarthians slipped into the relegation zone in Division Five following a 48-7 defeat at the hands of league leades Brecon Athletic.
In the WRU Women's Championship, Old Penarthians completed a league double at lowly Gwernyfed on Sunday, winning 39-0.
Next weekend's fixtures
WRU Division One Cup quarter final
Aberavon Green Stars v Penarth
WRU Division Two Cup quarter final
Cowbridge v CR Rygbi Caerdydd
Admiral League Division One East Central
Barry v Llanishen
Division Three East Central
Cilfynydd v Llantwit Major
Dinas Powys v Fairwater
Division Five East Central
Old Penarthians v Glyncoch
WRU Women's Championship
Senghenydd v Old Penarthians (Sunday)
Dinas Powys run in 21 unanswered points in second half against Gilfach Goch
Barry Youth overcome slow start to beat Beddau in Cardiff Division 2
Barry Rugby Football Club has lodged plans for extensions to its clubhouse and other works
Missed chance proved Barry's downfall against Caerphilly
Barry RFC Youth lose to Llandaff in Cardiff Rugby 2 League
Barry RFC girls coach recognised by Cardiff Rugby Community Foundation
Barry Town United end 26-year wait to lift Nathaniel MG Cup
Welsh legend Max Boyce and record-breaking footballer Jess Fishlock honoured at St David Awards
