Defending champion Rory McIlroy blamed agonising toothache after pulling out of the Honda Classic midway through a second round that was becoming embarrassing.
The Northern Irishman, ranked number one in the world, began on the back nine at the Palm Beach Gardens course and played his opening eight holes of the round in seven over par. He then found the water at the 18th - his ninth hole - and immediately quit the tournament.
"I sincerely apologise to the Honda Classic and PGA Tour for my sudden withdrawal," he said in a statement on pgatour.com. "I have been suffering with a sore wisdom tooth, which is due to come out in the near future."
He continued: "It began bothering me again last night, so I relieved it with [painkiller] Advil. It was very painful again this morning, and I was simply unable to concentrate. It was really bothering me and had begun to affect my playing partners."
He was playing in a group with Open champion Ernie Els and American Mark Wilson.
McIlroy added: "I came here with every intention of defending my Honda Classic title. Even though my results haven't revealed it, I really felt like I was rounding a corner.
"This is one of my favourite tournaments of the year and I regret having to make the decision to withdraw, but it was one I had to make."
The 23-year-old has struggled to rediscover the form that has elevated him to the top of the world rankings so far in 2013, highlighted by his first-round exit at the Accenture Match Play Championship to Ireland's Shane Lowry last week.
The PGA Tour reported it was the first time McIlroy has withdrawn during a tournament.
American Michael Thompson led on eight under par in the closing stages of his second round, two shots ahead of Australian Geoff Ogilvy and England's Lee Westwood who were his nearest challengers.