Rory McIlroy shot seven over par on the final eleven holes en route to a four-over-par opening 76 at the BMW PGA Championship at Wentworth.
The world number two opened his round with three pars before moving to three under par following an eagle at the fourth hole, followed up by a birdie on the fifth.
But it all started to go wrong for the four-time major winner on the eighth hole as McIlroy began a run of three bogeys in a row, and while he bounced back with a birdie on 12, further bogeys followed on 13 and 15 to move over par.
Worse was to come for McIlroy as the Holywood native posted a double-bogey on 17 before finishing on the final hole - McIlroy played 13 shots on the final two holes.
Playing partner Shane Lowry had a much less dramatic opening round at the English event as he posted a level-par 72. The Open champion had two birdies and two bogeys, including a six on the par-five 18th.
Padraig Harrington finished a shot further back with an opening-round 73 at the former Ryder Cup course.
Paul Dunne had a horrible day, shooting an eight-over 80 that left him rock bottom on the leaderboard.
The Greystones man carded seven bogeys and two doubles though at least managed to finish with a pair of birdies.
England's Matt Wallace believes his decision to part company with caddie Dave McNeilly is paying dividends after claiming the first-round lead.
Wallace carded an eagle and five birdies in a flawless opening 65 to enjoy a one-shot lead over former Open champion Henrik Stenson and Spain's Jon Rahm, with Justin Rose a shot further back.
Wallace was heavily criticised on social media for berating McNeilly towards the end of June's BMW International Open, where the defending champion twice found water on the 72nd hole as he chased a birdie to force a play-off.
The 29-year-old Londoner initially cleared the air with McNeilly and they worked together at the Open at Royal Portrush - where Wallace played alongside Tiger Woods for the first two days - but the split came four days after the World Golf Championship event in Memphis.
"It was the hardest decision I've had to make in my career," Wallace said. "He's done so much for me.
"He's got me to where I am today but it was a time and a decision that I wanted to be done and change something up.
"I didn't want to keep being like that with Dave and Dave like that with me. Dave is 67 and he wants to improve every day and that is why he was my guy for so long. He was great for me and I am sure I pushed him on as well.
"I don't think I want to change too much of me, I want to keep the fire. Around the Open I was changing my emotions inside and that was affecting the way I played.
"I hope I don't have to make any decisions ever like that again, but it's a business and it's what everyone keeps telling me. There are plenty of guys out here who sacked many a caddie and this is my first one. I wouldn't say it was a sacking, it was a parting of ways.
"Sometimes you need to make those hard decisions to go forward. I felt like it was the right one and it is producing some good stuff at the moment."