Adam Scott fired a course record 62 to take the lead after the first round of the Australian Open in Sydney.
Scott is looking to become only the second player to land the Australian PGA, Masters and Open title in the same season, and at three shots clear is bang on course for the hat-trick.
The US Masters champion had a strange round, birdieing the first six holes, parring the next eight, before finishing strongly with four more birdies.
"It was a beautiful day for golf, I came out hitting great shots and didn't have much work to do to clean them up in the first five holes and had a nice putt on my sixth hole and I was really rolling at that stage," he said.
"But I think I've gone through a rollercoaster of emotion out there today from cruising after six holes to having to work pretty hard.
"Nothing much was going my way, I missed a green, felt like my swing was leaving me again, it's just amazing how in 18 holes you can do a 360 degrees of emotion and mood swings and everything."
Canadian Ryan Yip shot 65 to tie the previous record and was in second place. David McKenzie had a 66 while two-time champion Aaron Baddeley was in a group with 67s tied for fourth.
Rory McIlroy, trying to win for the first time this year, shot 69, seven behind Scott. The Northern Irishman made the turn at two-under, bogeyed 11 and 12 but had three birdies in his final seven holes, including on the 18th.
He took 29 putts and admitted he was disappointed at his return.
"I drove the ball pretty well off the tee but just didn't get any reward on the greens," he said. "I missed three short ones and that was just wasteful as I felt it could have been a lot lower, given that I am driving the ball the best I feel I ever had.
"It's just a matter of being more efficient and putting better, and that's really it as I only played the par fives in one under par, and the way I am driving it, I should be playing those in four under."
Kevin Streelman, who played with Matt Kuchar on the runner-up American team in last week's World Cup at Royal Melbourne, shot 70 playing in the same group as Scott and Jason Day, who also carded 70.