Remarkably the 40-year-old Kiwi has now gone 54 holes without a single bogey, with his only blemish a double-bogey six on the final hole of his second round, alongside 21 birdies.
Geary shot a four-under 68 on Saturday to move to 19 under, well clear of former NSW Amateur champion Austin Bautista.
The 28-year-old Bautista had four birdies in his last seven holes - somewhat offset by a double-bogey six on the 14th - to lock in his spot in the final group on Sunday.
Young amateur star Declan O'Donovan birdied the closing hole on Saturday to improve to outright third at 14 under.
When he arrived at 13th Beach this week, Geary's main aim was to fine-tune his preparation for the New Zealand Open later this month.
But now the immediate focus has changed to claiming a first win on the Australasian Tour in 12 years.
"I sort of wanted to do a bit more technique work to try and test it under pressure," said Geary.
"But I've got myself right into contention so first things first - I've got to try and win rather than try and improve for then.
"It was great to play under the pump.
"It's always good to do that no matter what and see what shows up."
With his partner now working full-time and two young children at home to look after, Geary has to balance his home and golf lives more than ever before.
"Any win these days anywhere is hard to get so you've got to celebrate them when you can," he said.
First-round leader Kade McBride surged right back into contention with a four-under 68 that lifted him into a tie for fourth at 13 under with fellow Queenslander Aaron Wilkin.
And it could have been even better for McBride as his eagle-putt attempt on the par-5 18th grazed the hole and just stayed out.
"I turned it around nicely coming into the back nine which was good," said the 29-year-old who went 62-73 across the opening two days.
"That was probably about as bad a score as I could have shot out there today.
"I had a few things not go my way like on 15 where I hit a really good drive which hit the top of the lip on the bunker and then had a dog bark on my back-swing.
"But it is what is is."
Early starters Todd Sinnott (64) and 2018 Vic Open champion Simon Hawkes (66) shot the low rounds of the day to improve to a tie for seventh at 11 under.