Barry Town United lost 3-0 to plate winners Swansea City in the Adran Premier - on a day when league honours were decided.
Stevie McCarthy Campbell's side had held the six-time champions to a succession of goalless draws during the league campaign.
But on a day when the Women's Euros trophy visited Jenner Park, the Swans found the breakthrough as they confirmed themselves as Plate Conference winners with two games to spare.
Barry will finish the campaign second in the conference - and sixth overall in the table.
It took just seven minutes for Swansea to go in front as Katy Hosford's corner kick was headed home by Jessica Williams past keeper Molly Arnesen - the first goal she had conceded against the visitors this season.
Stacey John-Davis further punished Barry for a defensive error to double the lead on 24 minutes, before helping herself to a brace eight minutes later. Hosford again provided the assist as the forward's cross looped into the far post past Arnesen.
Danielle Broadhurst had a fourth for Swansea ruled offside before half time, and although Barry improved in the second half, chances were few and far between as the visitors held out to clinch the Adran Premier plate.
Away from Jenner Park, Cardiff City were crowned champions for the third season running after beating The New Saints 3-1.
The Bluebirds, under manager Iain Derbyshire, have been beaten just three times so far this season, having overcome the loss of key players before outseating The New Saints on their way to another title.
They'll also be the only top flight club in the Welsh capital next season after Cardiff Met's relegation was confirmed following a 2-1 defeat at Aberystwyth.
The Archers, who have won the Welsh top flight six times, helped to nuture the likes of Sophie Ingle and Alice Griffiths - but they've suffered a dramatic slump in form and are still waiting for their first league win after 18 games this season.
With the season effectively over, Barry will look to bow out on a high, having already secured their spot in the Adran Premier for next season after gaining a Tier One licence from the FAW.
Ironically, they welcome Cardiff Met to Jenner Park next Sunday before travelling to Cyncoed for the finale on April 13th.
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