By Gene Cherry, Reuters

World number one and defending champion Rory McIlroy walked off the course and withdrew from the Honda Classic after dropping seven shots in his first eight holes on Friday while suffering with severe pain from a wisdom tooth.

"It began bothering me again last night," McIlroy said in a statement. "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 later tweeted that the pain had been too great to allow him to play. "A tough day made impossible by severe tooth pain. Was desperate to defend title but couldn't play on. Gutted."

The PGA Tour said it was the first time the Northern Irishman had withdrawn from a tournament.

McIlroy shot an even-par 70 on Thursday in the opening round at PGA National before a triple bogey, a double bogey and two pars on Friday morning.

After hitting his approach shot into the water on the 18th, his ninth hole of the day, McIlroy walked off the course with his coach and caddie.

Beginning play on the 10th hole, McIlroy struggled from the start. He nearly hit his approach to the 11th hole into the water before chipping through the green and making a double bogey.

Two holes later, he made another bogey after driving to the right and being forced to lay up. He missed a six-footer to save par.

On the par-four 16th, McIlroy hit his tee shot into the water, took a drop, then hit another into the water before carding a seven. He then three-putted to go seven over after eight.