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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Dry with clear spells, with most southern and eastern areas having clear skies.
Wales manager Chris Coleman says his side can't get caught up in the 'fantastic atmosphere' ahead of tomorrow's Israel match.
A fairly cloudy start soon clearing south, allowing brighter conditions in the north to spread to all parts through the morning.