Tiger Woods endured a difficult return as he shot a four-over 75 in the first of the PGA Tour's play-off events at Liberty National in New Jersey.
Woods was playing his first round since missing the cut in The Open last month.
He recorded five bogeys and one double bogey to lie 13 strokes behind early leader Troy Merritt, who fired a 62.
Northern Ireland's Rory McIlroy was three shots off the lead after a six-under 65 with England's Danny Willett a further shot back.
Scotland's Russell Knox also finished on five-under alongside 2018 Masters champion Patrick Reed.
Woods, 43, who had spinal fusion surgery in April 2017, was only able to practise chipping and putting in Wednesday's pro-am.
After Thursday's round he said his back was "a little bit stiff, but that's just the way it's going to be".
Thankfully from Woods' point of view, there were far fewer spectators on hand to witness his struggles than normal. Following bad weather the day before, spectators were not allowed in until 10.00 local time, at which point he had almost completed his first nine holes.
The 43-year-old has played a very limited schedule since he won the Masters, with this being only his fifth start since that Sunday in April.
But he did not look comfortable and the poor round followed on from his struggles at Portrush in the The Open, where he had rounds of 78 and 70 to miss the halfway cut by five strokes.
"I didn't hit any good shots and didn't make any putts," Woods added.
It is nearly four months since Woods won the Masters to record his 15th major title, 11 years after his previous victory.
His fifth Green Jacket capped a comeback from four operations on his back which saw him drop to world number 1,199.
Woods has said he "could barely walk" before surgery and his children had seen golf cause "pain".
But in an interview with CBS on the eve of the Northern Trust Open, he opened up on what it meant to have his children, daughter Sam, 12, and 10-year-old son Charlie, waiting for him as he came off the 18th green at Augusta.
"I just wanted them to understand what daddy does, that he is not that YouTube golfer," said Woods.
"They see highlights of that guy, but I'm not that guy. I can still do it. For them to see it, feel it and feel the electricity of the crowd was awesome.
"To see Charlie first, then my Mom and to hug Sam, it gives me chills just thinking about it."
Woods added that the Masters victory had changed his children's perception of him as a golfer.
"They were both very hesitant about this golf stuff. They only remember the bad times. They associated golf with pain," he said.
"They are excited I am happy and playing again and I am doing something I love. They are seeing that in me.
"But they are worried about me because they don't want to see me hurt again."