Golf pro Rory McIlroy has taken the lead on a tough day for star Tiger Woods at the start of the 104th PGA Championship.

The Northern Irishman played a round of 65 at the Southern Hills Country Club in the US state of Oklahoma on Thursday (local time), staying five strokes under par.

Woods, who completed the first lap together with the Northern Irishman and Jordan Spieth, stumbled after a very good start and clearly had problems with his operated leg.

In his second PGA tournament since the serious car accident, he ended up with a round of 74 and, like Martin Kaymer, who needed 76 shots, has to worry about the cut on Friday.

Alex Cjeka played a round of 72.

"My leg didn't feel as good as I would have liked," said Woods after the start.

Two early birdies had the fans cheering, but after that not much worked out for the 15-time major winner.

"I just can't strain it.

Straining hurts, pulling the trigger hurts, running hurts, turning hurts," he said with a wry smile.

Woods had finished his comeback at the Augusta Masters in a remarkable 47th place under the circumstances and confidently said before the start in Tulsa that he believed he was stronger than he was in April.

McIlroy, on the other hand, was able to give information about day one with satisfaction.

"It felt very good," he told US television.

"I came here in good shape, so I knew my game was there and it was just a matter of playing my game."

Going into Friday's second round, McIlroy has a one-shot lead over Americans Will Zalatoris and Tom Hoge.

Justin Thomas is two strokes behind in tied fourth place.

The Masters winner Scottie Scheffler, who was so outstanding recently, stumbled a bit and is one stroke over par in shared 38th place.