He then withdrew, later saying he was bothered by tooth pain.

"I have been suffering with a sore wisdom tooth, which is due to come out in the near future," a statement by McIlroy read. "It began bothering me again last night, so I relieved it with 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."

According to the Associated Press, though, physical pain wasn't the only factor in McIlroy's decision.

"There's not really much I can say, guys," the AP quoted McIlroy as saying in the parking lot. "I'm not in a good place mentally, you know?"

McIlroy, who shot an even-par 70 in the tournament's opening round, struggled in cold, wet conditions Friday. After starting the day tied with 19 other golfers for 61st place, McIlroy collected a double bogey on No. 11, a bogey on 13 and another bogey on 17.

His worst hole was the par-4 16th, where McIlroy sent two balls into the water before finishing with a triple bogey that sent him plummeting into a tie for 136th place.

Both of his playing partners, former Honda champs Ernie Els and Mark Wilson, said neither noticed McIlroy to be in pain.

"He wasn't playing the way the world No. 1 plays normally," Wilson said. "He was upset with his golf, and I guess he had enough for the week."

Added Els: "That's the last thing he wants to do is walk off. Obviously something was seriously bothering him and he was not going to make the cut, and probably didn't want to continue playing that way."

Friday's withdrawal was McIlroy's third early exit this year. He missed the cut in January's Abu Dhabi Championship, and was eliminated in the first round of last week's World Golf Championships-Accenture Match Play Championship.