Halfpenny kicked another nerveless three points, after the Lions earned a further penalty at the scrum.
When the Australian forwards couldn't live with the Lions at scrum time yet again, prop Ben Alexander was sent to the sin bin.
Halfpenny again made no mistake, to extend the Lions' lead to 19-3 after 26 minutes.
More top news
Organisers say there will be increased security at the Urdd National Eisteddfod, which began in Bridgend today.
Any remaining heavy or thundery showers will clear eastwards this evening.
Over 70 firefighters are currently tackling the fire, which is now confirmed to be at a scrap yard.