Adam Scott is four ahead of Rory McIlroy going into the final round of the Australian Open after a four-under 68 on Saturday.
Scott needs victory at Royal Sydney to complete his country's 'triple crown' having won the Australian PGA and Masters in recent weeks.
Starting the day two ahead of nearest challenger McIlroy, Scott moved clear with a front nine that featured four birdies, including three in a row from the seventh.
He started the back nine with a bogey but picked up further shots at the 14th and 18th to get to 16-under-par overall.
"It's an exciting position to be in, obviously a great chance to win my national championship tomorrow," said Scott.
"And then also win the three events down here which is an unbelievable spot to be in. If you'd told me a month ago, I wouldn't have believed you.
"One round to go but a lot can happen. It's a phenomenon playing behind me and I'm sure he's going to throw plenty at me... but as long as the eye stays in with the putter, I think I should hold on."
Northern Ireland's McIlroy, the former world No 1 without a tournament win in 2013, was five behind after a bogey at the fourth was followed by a double-bogey at the next.
But he rallied with four birdies and no bogeys during the remainder of a two-under 70 that left him on 12-under-par, although he did miss a short birdie putt at the 18th.
"I played a good back nine, it could have been a couple better, I felt I left a couple out there," said McIlroy.
On his chances of catching Scott on Sunday, he added: "(It's possible) on this golf course, where there can be a lot of two-shot swings and someone makes a couple of pars and someone gets off to a fast start and makes a birdie and an eagle and you're right back in it.
"There's plenty of chances out there and it's just a matter of taking your opportunities when they come."
The final round is set up for a head-to-head battle as McIlroy is four ahead of a trio of Australians sharing third place, Max McCardle (69), Matt Jones (72) and Richard Green (73).