The home side struggled to build any sort of momentum in the opening 40 minutes, finding themselves 13-3 down at the break.
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A yellow card issued to Scot, combined with Tom Prydie's successful penalty, gave the Welsh outfit some hope, but they struggled to capitalise on the man advantage and soon fell further behind when Roberts split the sticks once more.
It was a different story following the restart, however, as both Richie Rees and Prydie crossed over in the corner to swing the game completely, while a second Welsh yellow, this time issued to Roberts, dented their hopes severely.
Just five minutes remained when a third player, replacement Ian Gough, was sent to the sin bin, but it mattered little in the end as Newport held out for the LV=Cup win.