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)
Talks to be held on Cardiff Rugby sale
Bombers beat Welfare to boost survival hopes
Llantwit reach WBS Cup quarter finals
Barry kick off Phase Two at TNS
Vale teams join in Cardiff clubs' day
Le Tour comes to Cardiff
Barry cruise into Cymru Premier Top Six
Barry prepare for Top Six decider
Llantwit away day frozen off
Cymru Premier: phase one finale postponed
Barry duo up for league awards
Five-try Dinas beat Gilfach Goch
Barry Ladies rout winless Ponty
Barry beaten by Nomads' fightback
