Johnson's 62 established a new course record for StoneWater Golf Club and was also a career-best. He shares the lead at 10-under-par 203 with fellow Australian Matthew Jones, who shot a 3-under 68 in his third round.
'I know it sounds cliche, but I tried to take it one shot at a time,' Johnson said of his record round. 'I really just tried to stay in the moment.'
Former PGA Tour winner and overnight leader Dicky Pride managed just an even- par 71 in his third round. He is alone in third place at 9-under-par 204. Matt Weibring (65), Tom Scherrer (67) and Scott Parel (66) share fourth place one stroke further back.
Johnson, who was tied for 38th place overnight, began his third round on the back nine. He opened with consecutive pars before three straight birdies from the 12th moved him to minus-4.
At the 625-yard par-5 13th, Johnson landed an 8 iron within 8 feet to set up birdie. He followed that by landing a 3-wood 2 inches from the hole at 14 to set up another birdie.
Johnson moved to 5 under with a birdie at the par-4 16th and he would remain there around the turn.
His bogey-free round -- one of three carded Saturday -- continued with consecutive pars at Nos. 1 and 2, and two straight birdies from the third moved him to minus-7.
Johnson then carded consecutive pars before setting up a 62 with birdies at his final three holes. He rolled in a 12-foot putt at the eighth, and sandwiched that with 5-footers at the 7th and ninth.
'Everything started going in today,' said Johnson, who will be looking for his first career win after missing the cut in nine of his 15 starts this year. 'I've been sick all this week, coughing and hacking, and I started feeling a little better today.'
Johnson's best finish in his rookie season was a tie for 21st at the BMW Charity Pro-Am in May. And with just $14,089 in earnings, he is 150th on the Nationwide Tour's money list.
'All in all I don't feel like I've played all that bad,' he said. 'I feel like I haven't played that bad all year, but I just haven't gotten a lot out of it.'
Jones, who was alone in second place overnight at minus-7, began his third round on the front nine and quickly moved further under par. He birdied No. 3 before carding an eagle at the par-5 fourth, where he set up a 25-foot putt with a 4-iron.
That moved Jones to 10 under, but he stumbled to the first of his two bogeys at the fifth to drop back to minus-9. Another bogey at 11 put him at 8 under, but Johnson recovered two strokes with birdies at Nos. 12 and 14 to get back to minus-10.
'I've never been in the last group on Sunday,' said Jones, whose best finishes on tour are a pair of fourth-place ties. 'It will be fun playing with Andrew. Hopefully we can pull each other along and play well.'
Camilo Villegas also fired a bogey-free round Saturday. He carded a 4-under 67 to share seventh place with David Morland IV (64), who shot a 6-under 29 on the front nine (his final nine holes). Morland's 64 would have been the course record if not for Johnson.