Three more Australians - Rod Pampling and left-handers Greg Chalmers and Richard Green - share second place at 4-under-par 67. Camilo Villegas, just one of three non-Australians in the top-35, heads a group of six players at minus-2.
Barnes got off to a good start with a birdie at the first, but stumbled to a double bogey at the third. His troubles continued as he bogeyed the fourth.
Things quickly turned around for Barnes. He ran off four straight birdies from the par-5 fifth to get to minus-2. The Australian parred the next four holes around the turn.
Barnes converted a birdie try at the 13th. He came right back with a birdie on 14 and made it three straight when he birdied the 15th. Barnes closed with three straight pars to finish at 6 under.
'It's just golf. We're out here to have fun,' Barnes said. 'You can't treat this game too seriously otherwise you'd go insane. I went out there and had a great time. If you're lucky enough to shoot a good score, well so be it.'
Villegas is tied for fifth at 2-under-par 69 with five Australians - Stuart Appleby, Aaron Baddeley, Anthony Gilligan. Brett Rumford and Shannon Beck.
New Zealand amateur Travis O'Connell is among a group of 13 players at 1- under-par 70. Among those at minus-1 are Anthony Painter, Stephen Leaney and Nick O'Hern.
Peter Lonard, the defending champion, stands in a tie for 24th place at even-par 71.