Penarth claimed an Admiral League scalp with a 25-23 win over Division One East Central champions St Joseph's.
The Bears marked their final home game by becoming the first team this season to beat the Cardiff-based club, who had already clinched the title.
Penarth's own hopes of being crowned champions had ebbed away - but they could still secure a top-three finish next Saturday, when they travel to Abercwmboi for the final game of the season.
In Division Two, Cowbridge's faint hopes of promotion were finally dashed by St Albans, who beat Cardiff Quins 26-20 to secure runners-up spot.
Cowbridge can still finish in third, but they'll face a tough challenge on Wednesday night (7pm ko) with the visit of champions Caerphilly, who retain a 100% record from seventeen games.
Llantwit Major signed off the Division Three campaign as they romped home to a 54-7 victory over relegated Tonyrefail.
Despite a points deduction, Major ended the season in a respectable fourth - while Wattstown clinched the title with CR Cymry Caerdydd promoted as runners up.
And Llantwit will be joined next season by Dinas Powys, who have already clinched back-to-back promotions but must wait to see if they'll go up as Division Four champions.
Ferndale could still catch them if they claim a bonus point win next Saturday at Brackla.
Finally, Old Penarthians round off their WRU Women's Championship season on Sunday when they take on Llantwit Fardre at home.
Plate honours for ex-Barry RFC junior
Lewis back in the Llantwit hotseat
Barry's Euro hopes dashed by Cofis
Barry's play-off push begins
Bombers' season of progress and missed opportunities
Stait resigns as Llantwit manager
Barry to face Cofis on play-off trail
Barry run riot for captain's farewell
Captain McLaggon to leave Barry Town United
Harriett aims for ice dance glory
Bombers defeated in Plate warm-up
Bombers well beaten by St Joseph's
Adran Premier: Barry sign off with Archers win
Barry reach play-offs after Nomads win
Llantwit beaten as Lansdown bows out
WRU takes over at Cardiff Rugby
Barry secure FAW licences for next season
