The US Masters champion shares the clubhouse lead with German Maximillian Kieffer.
Both are behind overall leader, Victorian Anthony Brown, who has leapt out of the blocks and is five under through seven holes.
Scott made a steady start after beginning his round at the 11th hole, managing just one birdie in his first eight holes in chilly but benign conditions.
But he brought the adoring galleries to their feet with birdies on the par 4 first, par 5 second, par 3 third and par 4 fourth to shoot to five-under.
Scott's main tournament rival American world number eight Matt Kuchar carded a 71 and is currently tied for 33rd.
It has been a cold and wet week in Melbourne but the rain has so far stayed away at the sandbelt course.
Leukaemia survivor Jarrod Lyle made an emotional return to golf when he teed off at 12.30pm (AEDT) in front of his hometown fans.
The Victorian is currently one under after three holes.
Having claimed the Australian PGA by four shots at Royal Pines on Sunday, Scott remains on track for the triple crown.
Birdie blitz fires Adam Scott into Masters lead
