A late stumble by South African golfer Louis Oosthuizen during his third round has opened the door at the Perth International at Lake Karrinyup.
The world No.21 lost his concentration and dropped two shots in his final three holes to finish at 15 under on Saturday and reduce his lead to three shots.
Four golfers, including Australians Jason Scrivener (11 under) and Brett Rumford (10 under) are within five shots of the 2015 Masters runner-up and within striking distance.
Oosthuizen produced seven birdies before the first of his two bogies at the 16th and looked to be running away to an uncatchable lead.
However, he lost concentration, he said, worrying about the where the hole was placed on the green.
"I lost a big of concentration on 16, worrying too much on the way about where the pin position was," he said.
"I can't say it was a fair pin position. It was right on a slope - there is no way you can really do anything with that hole.
"So it was a matter of thinking about other things on those holes besides what I am supposed to do."
"Those things happen. As long as they don't happen when you are tied for the lead with three shots to go."
Joint overnight leader Peter Uihlein is in joint second place on 12 under after a round of 71.
He may well rue his bogey on the 18th hole and the six shots he took on the 135m par-three 12th when he hit his tee shot to the back of the green and struggled to recover before taking two putts to finish.
Rumford, who started the day tied with the American in first place, produced back-to-back eagles late in his third round to stay in touch.
The chip shot he holed out of the bunker on the 14th, which also had to work along a tough green, was arguably the shot of the day.
However, he was wayward early in his round. He recorded three bogies and a birdie in his first four holes to drop from 11 under to nine under.
More dropped shots at the ninth and 13th left him at seven under.
He finished with six bogies, two eagles and a birdie to card an inconsistent round of 73 and go into the final day at 10 under and in fifth place.
Australia's Marcus Fraser and Frenchman Romain Wattel were the big movers during the round, each carding 65.
Wattel is tied with Uihlein in second place on 12 under after a bogey-free round, and Fraser is three shots further behind in a tie for sixth at nine under.