Australian fly-half James O'Connor finished a jinking run with a try in the very last play of the first half, to narrow the scoreline to 19-10.
The Lions lead at the break thanks to Alex Corbisiero's early try, and 14 points from the boot of Leigh Halfpenny.
Australia could have been ahead, but turned down five opportunities to kick penalties for goal in the first period.
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A yellow warning of ice and snow has been issued by the Met Office. It covers many parts of Wales from 18:00hrs tonight.
A burglar who ate an entire tub of ice cream before falling asleep in the house he was raiding has been jailed.
It will remain cold this afternoon with a risk of wintry showers. Winds remain strong. Best of the brightness through eastern counties.