GOLD COAST, 11 Dec 2014 (AFP) - The three-time US PGA Tour winner topped the leaderboard following a rain-affected first day at Royal Pines, where half the field are yet to complete their opening rounds.
Weekley led a group of five players on four-under including defending champion and world number three Adam Scott.
The American's month-long stay in Australia has included equal 15th place finishes at the Australian Masters and Australian Open.
Weekley carded five birdies, a bogey and an eagle around the revamped Royal Pines course.
"I had 146 (yards) into the hole, was kind of in between clubs and I just figured I had a breeze a little bit into us ... took an eight-iron and choked it down a little bit," Weekley said of his eagle at the 17th hole.
"As soon as I got up in the air, got flying towards it then one hop and it went in the hole."
Scott also made eagle on Thursday at the par-five 15th and was happy to notch the first under-par first round of his Australian swing of tournaments.
He expects he will have to keep scoring low to defend his title.
Scott is joined at four-under by several players including youngster James Marchesani and Korean Jin Jeong, who was through 12 holes when play was called off as a storm rolled in.
Leading scores after the opening round of the Australian PGA Championship at Royal Pines (par-72) on the Gold Coast on Thursday (Australia unless stated):
66 - Boo Weekley (USA)
68 - David Smail (NZL), Adam Scott, Wade Ormsby, James Marchesani, Craig Hancock
69 - Jarrod Lyle, Brad Kennedy, Scott Strange, Nathan Green, Neven Basic, Ratchapol Jantavara (THA)
70 - Josh Geary (NZL), Ryan Fox (NZL), Michael Hendry (NZL), Peter Cooke, Xinyang Li (CHN), Kevin Conlong, Chirat Jirasuwan (THA)
71 - Greg Chalmers, Josh Younger, Brendon De Jonge (ZIM), Jake Higginbottom, Mark Brown (NZL), Alistair Presnell, Adam Stephens, Paul Donahoo
72 - Scott Stallings (USA), Scott Gardiner, Michael Sim, Mark Gilson, Leigh Deagan, Steven Jones, Brad Shilton (NZL), Matthew Ballard, Michael Choi, John Young Kim (USA)
Selected scores:
73 - Martin Kim (ARG), Ryan C Carter (USA), Zhou Guowu (CHN), Zhu Weiyu (CHN)
74 - Wisut Artjanawat (THA), Duan Chenxiao (CHN)
75 - Kim Tae-Woo (KOR), Park Deuk-Hee (KOR)
76 - Tommy Mou (TPE), Michael Im (KOR)
77 - Choi Joonwoo (KOR)
79 - Dou Zecheng (CHN)