Welsh centre Jamie Roberts - facing Australia for the first time this summer due to injury - has scored the Lions' fourth try, taking a pass from replacement Conor Murray before galloping home.
Halfpenny makes it another seven points, and the Lions start to celebrate a series win.
More top news
The Royal London One-Day Cup match being played in Cardiff has been abandoned due to a 'dangerous pitch'.
A series of crashes on the A470 have led to traffic disruption
A largely dry and warm afternoon, but a muggy night to come with showery outbreaks.