American golfers Dustin Johnson and Bo van Pelt were just off the pace behind a leading quartet in the $2 million Perth International at the Lake Karrinyup course on Thursday.
Australian duo Clint Rice and James Nitties led after the opening round at four-under 68, along with South Korean Jin Jeong and Sweden's Peter Hedblom.
World number 21 Johnson shot a three-under 69 with van Pelt one stroke further adrift.
England's 12-time European Tour winner Paul Casey (four-over) and rising South African star Branden Grace (one-over) had days to forget.
Australians Nick O'Hern, Brady Watt, Nick Cullen and Dimitrios Papadatos were among a large group of players at three-under.
The Perth International, Australia's richest tour event, is the nation's only tournament to be co-sanctioned by the European Tour and the PGA Tour of Australasia this season.
Johnson, who was forced to cancel a media conference on Tuesday due to a cold, said he was feeling better.
"I'm fine. I'm feeling way better than I was," Johnson, 29, said. "I've just got a little bit of a cough which is OK. I'm back to where I feel good enough to play good golf."
The American said he was satisfied with his round, which included five birdies and three bogeys.
Defending champion Van Pelt won at Lake Karrinyup last year after a battle with countryman Jason Dufner.
Jin, who moved from South Korea to Australia seven years ago when he was just 16, produced the highlight of the day when he holed a 167-yard shot on the par-fourth 18th for eagle.
"I didn't think it was going to go in," Jin said. "I thought it would be another three or five feet. But people started clapping and yelling, so yeah, quite happy."