Cameron Smith's bid for a third successive Australian PGA Championship title got off to a rocky start as the double-defending champion slumped to a two-over 74 at the Royal Pines Resort on the Gold Coast.

The world number 53 will start the second round seven strokes adrift of compatriots Lucas Herbert and Brett Rankin, who each opened with five-under-par 67s to lead the A$1.5 million event co-sanctioned by the European Tour.

Smith, who started on the 10th hole, plunged down the leaderboard in a horror run of three holes with a double-bogey on the second and back-to-back bogeys at the third and fourth.

Smith said fatigue had played a part in his poor round after a big week at the Presidents Cup where he was a member of the International team that lost to the United States at Royal Melbourne on Sunday.

"I'm just tired," he told reporters.

"Just a long couple of weeks and it was as easy as it's going to get out there this morning, so it was pretty disappointing to shoot what I shot."