A try from fly-half Jonathan Sexton - and another Leigh Halfpenny conversion - put the Lions clear again heading into the final quarter.
Sexton touched down after receiving the final pass from Halfpenny in a slick Lions move in the left corner.
Australia had closed the gap to just three points early in the second half through two Christian Leali'ifano penalties.
Halfpenny added another penalty of his own.
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Tributes have been paid to an ambulance driver killed in a crash with another ambulance in North Wales.
Tonight is expected to be clear and dry - though some parts of Wales will experience frost.
The RSPCA said the animal had found himself in "quite a predicament" after becoming trapped in the tight space.