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.
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Swansea City failed to capitalise on last weekend's dramatic win over Crystal Palace, as they fell to a heavy 5-0 defeat away at Tottenham.
Post Office workers and managers have held a third strike in a long-running dispute over job losses and pensions.
After a cloudy start it will be a dry day today. The cloud will break up this afternoon, with some bright or sunny spells developing