Defending champion Tiger Woods carded a one-under 71 as he struggled with his form in his first appearance of 2006 at the Buick Invitational in California.
Woods, who last played in mid-December, hit only one fairway in his first round to finish six shots off the pace and admitted: "I really struggled."
American Brandt Jobe and Frenchman Thomas Levet share the lead after both fired seven-under-par rounds of 65.
England's Brian Davis stayed in touch with a 68 while Luke Donald shot a 75.
World number one Woods spent part of his lay-off skiing, but much of it simply resting and spending time with his father Earl, who continues to battle cancer.
He returned to action with a new Nike driver but refused to blame his equipment on his disappointing display in San Diego.
"The driver is fine," said the Masters and Open champion. "It's the dude holding it.
"I knew what I was doing, I just couldn't stop it. I was protecting a left hook so I hit everything right.
"I've missed the rush of trying to shoot low numbers and win tournaments"
Three successive bogeys late on did the damage to Woods' card, although he did manage to finish with a birdie.
Australian Stuart Appleby produced the crowd-pleasing shot of the day as he holed out with a wedge for an eagle at the eighth.
He is among was among a group of nine players tied for third after carding rounds of 66.
The Buick Invitational is played over two courses - the North and the South, which is much longer.
Jesper Parnevik was one of just five out of the top 40 finishers who played on the tricky South Course, carding a useful 67.
"Give me a five under on the South Course tomorrow and then we'll talk," said joint-leader Jobe, after hearing about the Swede's score.
USPGA champion Phil Mickelson opened with a 71 after mixing five birdies and four bogeys on the South Course.