Rory Mcilroy (AP Photo)

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McIlroy struggled through the back nine on Friday, his opening nine holes of the round, and hit his approach at the 18th into water. He then walked off the course and quickly departed the grounds with his coach and caddie.

"I sincerely apoloize to The Honda Classic and PGA Tour for my sudden withdrawal," McIlroy said. "I have been suffering with a sore wisdom tooth, which is due to come out in the near future."

VIDEO: Honda Classic - highlights

It was the first time in his career that McIlroy has withdrawn from a tournament and it comes as the 23-year-old from Northern Ireland struggles to find his form after switching to Nike equipment for this season.

McIlroy is a 6-1 co-favorite with 14-time major champion Tiger Woods in next month's Masters, but the tooth issue could dim his bid to add to a major haul that includes the 2011 US Open and 2012 PGA Championship.

"It began bothering me again last night," said McIlroy. "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."

McIlroy gave no hint as to how the injury might impact his plans for playing in the weeks leading up to the year's first major tournament at Augusta National.

He had plans to play next week in a World Golf Championships event at nearby Doral and the Houston Open in the week before the Masters, but gave no hint if that was still the case in his statement, or in a later Twitter posting.

"Apologies to all at the Honda. A tough day made impossible by severe tooth pain," McIlroy tweeted. "Was desperate to defend title but couldn't play on. Gutted."

Especially gutting for McIlroy was the fact the pain flared as he was trying to defend the title he won a year ago to put himself atop the world rankings for the first time in his career.

"I came here with every intention of defending my Honda Classic title," said McIlroy. "Even though my results haven't revealed it, I really felt like I was rounding a corner. This is one of my favorite tournaments of the year and I regret having to make the decision to withdraw, but it was one I had to make."

McIlroy endured a horror-show start on Friday alongside South Africa's Ernie Els, the reigning British Open champion, and American Mark Wilson.

At the par-4 11th, he nearly put his approach into the water, then chipped across the green on his way to a double bogey.

On the par-4 13th, McIlroy went way to the right off the tee and missed a six-foot par putt.

After a pair of pars, he put his tee shot into the water at the par-4 16th, then took a drop and put his third shot into the water as well on the way to a triple bogey.

At the par-3 17th, the Northern Irishman three-putted from 42 feet for bogey to stand seven-over par for the round through eight holes.

McIlroy, who missed the cut in his first 2013 start at Abu Dhabi and lost in the first round of the WGC Match Play Championship last week, opened with a par-70 on Thursday but admitted he was still working on his timing and adjusting to his new clubs.

"It's hard to commit to the shot that you need to play every time," McIlroy said Thursday. "I felt like I hit the ball OK, not as good as I can, but it's getting there."