Teeing off in just the third group of the day, the 48-year-old was never headed after amassing nine birdies against a lone bogey to set the clubhouse target early.
At 5-under fellow veteran Brett Rumford and rookie Daniel Hoeve were his nearest challengers, a logjam of players at 4-under and sharing fourth.
On a day when 42 players broke par defending champion Curtis Luck was not among them, the rookie professional signing for an even par 72 alongside promising amateur Minwoo Lee.
Newly qualified LPGA member Hannah Green got off to a fast start with two birdies in her first four holes but battled the rest of the round to eventually sign for a 2-over 74 and a share of 82nd position.
But the biggest surprise was perhaps the play of Leaney, the man himself admitting a poor range session before teeing off had him less than confident on the first tee.
“When I warmed up I literally did not hit one shot in the middle of the clubface,” he told the PGA’s website.
“So I wasn’t really sure what was going to happen. But it suddenly it clicked. I made a good swing down nine, the first hole and just sort of kept it going.”
With momentum and confidence on his side Leaney made the most of home ground advantage at what is his home course when he is in Western Australia.
“I just played smart,” he said. “Having played here so many times, it doesn’t always help but I know that you don’t have to go crazy off the tee around here. You’ve just got to keep it on the fairway.
“I think a lot of guys get caught up trying to blaze away around here but it’s not really the way to play it.”
Five times a winner of the tournament Leaney isn’t getting ahead of himself after one round but said he would love to claim the title for a sixth time so his kids could see him win.
“It would mean a lot to win again because I haven’t won for such a long time,” he said.
“Both my kids say: ‘Well, you haven’t won for a while dad, would you win a tournament again so we can see you hold a trophy?’
“But that’s a long way off. It’s a good start and when I warmed up on the range this morning I really didn’t know what I was going to shoot.”
Fellow Royal Perth member and European Tour stalwart Brett Rumford played alongside Leaney and the pair dragged each other along, Rumford also recording just one bogey in his 5-under 67.
Despite his score, however, the winner of the World Super 6 tournament earlier this year was less than pleased with his play.
“I didn’t drive it well and this golf course is all about driving,” he said.
“I left a lot of shots out there because I just didn’t give myself the opportunities with wedges in my hand.
“I will be working on my driver this afternoon to get it going for tomorrow.”
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