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
Well a fabulous day today has ended on a spectacularly soggy note for some! Heavy rain, hail and thunder will work northwards overnight!
The Talyllyn runs from Tywyn, near Aberdovey, for more than seven miles to two villages in the south Gwynedd countryside.
Homes in parts of Tonypandy and Llwynypia are without water this evening due to a burst water main at Cilfynydd.