The 21-year-old was one stroke clear of Aron Price, Andrew Tampion and Scott Gardiner, who landed himself a new $70,000 Lexus with a spectacular hole-in-one on the 176m par-3 11th hole.
World No1 Rory McIlroy carded a two-under 69 to be well in the mix in a share of fifth spot, but Adam Scott made a poor start in his quest for a second national championship.
Opening with a double-bogey six on the first hole, Scott went out in 40 on the front nine before clawing back two shots coming home to be seven behind Spieth after signing for a three-over 74. The world No3 was nevertheless still in danger of missing the halfway cut.
Languishing in a tie for 86th, Scott will likely need to rebound with a red number at The Australian this morning to earn a weekend tee time.
Richard Green, Adam Crawford, Michael Hendry and teenage amateur star Ryan Ruffels were all sharing fifth with McIlroy at two under.
Crawford had an eagle on the par-5 14th, as well as four birdies and four bogeys, but McIlroy's round wasn't anywhere near as eventful.
Starting his title defence from the 10th tee, the world No1 turned in even par after notching just one birdie on his opening nine, at the 459m 14th. He handed the shot straight back when unable to save par from the trap on the par-3 15th before collecting up-and-down birdies on the first and fifth holes - his 10th and 14th for the day - to climb to two under.
McIlroy again dropped a shot after finding the sand with his approach on the seventh but, after labouring most of the morning, the Northern Irishman stiffed an approach shot at the last to briefly grab a share of the clubhouse lead.
Playing alongside McIlroy, Matt Jones - a lifelong member of the course - struck a spectator in the head with an errant drive on the second-last hole.
There was concern for the fan, with medics called, but he appeared okay and received a signed ball from the US PGA Tour star, who refused to blame the incident for his late implosion in a disappointing round of 76.
- AAP
