Ernie Els shredded the back nine at Lake Karrinyup for the second successive round to extend his lead into the halfway stage of the Johnnie Walker Classic.
The South African, who led overnight on eight under, reached the turn in level par for the day before carding another 29 - including his second eagle on the par-five 15th - to finish on 15-under par, four shots ahead of Greg Owen and Robert Allenby.
Paul McGinley, the only Irishman in the field, failed to capitalise on his good start and dropped off the pace somewhat with a second round 71 to be in a group on six-under alongside Ian Woosnam.
It was a masterful comeback from Els, who is chasing his fifth tournament win in six starts, after he had found the water on the par-five fifth for a bogey and struggled to find his rhythm early on.
Els birdied the 11th and then landed his tee shot to within inches on the par-three 12th to pick up another birdie.
He then carded a pair of threes before and eagle on 15 elevated him three shots clear of the pack on 14-under-par.
His homeward 29 and seven-under-par round of 65 was sealed with a 33 foot putt on the last.
"That was nice," he said. "I didn't expect that to go in. I wasn't trying to shoot a 29, it just happened. I guess I have to thank the architect.
"I enjoyed it, it all came together for me."
Els leapfrogged back over Owen and Allenby, the number one Australian, who had both shot stunning second round 64's.
"At the moment Ernie is really tough to beat at whichever tournament he tees up in," was Allenby's compliment to the big South African.
Defending champion Retief Goosen shot a seven-under-par 65 having begun the day on level par, but was still disappointed with his showing. He felt the course record was up for grabs.
"That was the worst I could have scored," said the South African who equalled the record of 63 last year. I felt like a 62 was definitely on."
Sergio Garcia reached halfway stage on level par after a two under round of 70 which included "a couple of stupid bogeys on the back nine".
Denmark's Soren Hansen was disqualified from the tournament after failing to turn up for his 9 a.m. tee-off, but there were cheers for Singapore's Mardan Mamat who aced the 219-yard eighth hole to register his first in competitive golf.
PA