Crowd favourite Phil Mickelson birdied the last to take a share of the lead after the first round of the USPGA.
US unless stated
-3 Trevor Immelman (SA), Ben Curtis, Stuart Appleby (Aus), Phil Mickelson, Rory Sabbatini (SA), Stephen Ames (Can)
-2 Steve Elkington (Aus), Bernhard Langer (Ger), Heath Slocum, Greg Owen (Eng), Davis Love, Retief Goosen (SA), Lee Westwood (Eng), Jesper Parnevik (Swe), Pat Perez, Ben Crane, John Rollins
He carded a three-under-par 67, the same return as Stephen Ames, Stuart Appleby, Ben Curtis, Trevor Immelman and Rory Sabbatini.
The form of 2003 Open champion Curtis was one of the biggest surprises of an eventful day, as he has been in dire form since his shock win at Sandwich.
The other big surprise was the poor display of Tiger Woods, who shot a 75.
Woods, attempting to win his third major this season, drove poorly on his front nine and putted badly on his back nine to find himself eight shots off the lead.
Defending champion Vijay Singh, the world number two, finished in style with birdies at the closing par-fives to sign for a level-par 70.
The 28-year-old Curtis, playing the kind of golf not seen from him since Royal St George's two years ago, fired a bogey-free 67 to equal Immelman's clubhouse target.
The pair shared the lead for most of the afternoon until Australia's Appleby and Mickelson matched them in the evening.
Sabbatini, another South African, birdied the last two holes to become the fifth player to reach the safety of the locker room on three under.
And with shadows stretching across the 18th green, Canadian Ames tapped in for birdie to make it a six-way tie for first.
Mickelson's results at this year's majors, including a 60th-place finish at the Open last month, did not suggest he was poised to add a USPGA crown to his 2004 Masters title.
"I feel more relaxed and confident this week than I did at the other majors," said Mickelson. "I feel a lot better about my game.
"I feel a lot more confident about where the ball is going."
The sextet are one shot better off than an 11-strong group on two under that includes world number five Retief Goosen, 2004 Ryder Cup captain Bernhard Langer, 1995 USPGA champion Steve Elkington and English duo Greg Owen and Lee Westwood.
For Curtis, Thursday's round was a hugh relief from his form this season. He has made only three of 16 cuts.
"Golf is a funny game. It can come and go at any time," said the 28-year-old American.
"Every golfer goes through a rough time in their career and I went through it in the last year or so but I'm going to try to work out of it and try to stay positive.
"I know in the long run I'll be a better player for it."
Curtis, who was a rank outsider when he stunned the golf world to win the Open, said the key to his fine start were long par putts on the 11th and 12th.
"I hit a couple of bad approach shots and I could have left one or two over after those holes," he said.
Immelman, however, was more surprised that the scoring has not been better.
"The scoring conditions are perfect, but it just goes to show there are 18 really strong holes on this course," said the 25-year-old, who was fifth at the Masters.
"Any one of them can bite you at any time."
Appleby had looked like improving the clubhouse target to four under but bogeyed the tricky eighth, his 17th, to return to three under.
Hal Sutton, the 1983 USPGA champion, and Justin Leonard, the 1997 Open champion, are among a large group on one under after opening rounds of 69.
Also on that score are Ryder Cup team-mates Luke Donald and Ian Poulter.