Llantwit Major began their Cymru South campaign with a 1-0 defeat to Trethomas Bluebirds.
Ben Stait's men came up against a tough test from the newly promoted visitors, who were crowned Ardal South East champions last season.
Llantwit suffered an early injury blow when Joel Woodington was forced off midway through the first half, shortly after one of his efforts struck the crossbar.
Veteran keeper Jack Lansdown denied both Leon Thomas and Gareth Tedstone from the penalty spot either side of the break.
But Trethomas finally broke the deadlock when Tedstone struck from close range on 72 minutes for their first goal in the second tier of Welsh football.
Major pressed hard for an equaliser in the closing stages but found the visiting defence hard to break down.
Llantwit turn their attention back to the Nathaniel MG Cup on Saturday, when they entertain 2019 winners Cardiff Met.
JD Cymru South results
Carmarthen Town 1-2 Goytre United
Cwmbran Celtic 1-3 Cambrian United
Llantwit Major 0-1 Trethomas Bluebirds
Newport City 3-1 Ammanford
Penrhiwceiber Rangers 0-0 Baglan Dragons
Pontypridd United 3-2 Afan Lido
Taffs Well 1-1 Llanelli Town
Trefelin 1-0 Caerau Ely
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Barry Town United rounded off their pre-season campaign with a 3-2 victory over Swansea City's under 21s.
Steve Jenkins' men have won five friendlies in a row, including last weekend's memorable 2-1 scalp of Newport County and a 5-3 thriller against Cardiff City's U21s.
Barry begin their competitive season next Saturday when Llanelli Town - last season's runners-up in the Cymru South - visit Jenner Park for the second round of the Nathaniel MG Cup.
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