Tiger Woods headed quickly to the range to work on his swing after a mediocre opening round at the Arnold Palmer Invitational.

Woods, seeking to preserve an unbeaten streak of more than six months, was unhappy with his iron play in benign morning conditions at Bay Hill.

He did not do any great damage to his chances, posting an even-par 70 to trail clubhouse leader Fred Couples by five strokes, but it clearly was not the sort of performance his fans have become accustomed to seeing.

"I just didn't feel comfortable with my irons," said Woods, who has won his past five official tournaments worldwide. "I missed some greens I don't normally miss, one with a sand wedge, one with a pitching wedge, mistakes I don't normally make.

"I just couldn't figure it out and I've got to do some work this afternoon. I have a sense of what I needed to do but still need to do the reps and make sure I get nice and comfortable for tomorrow."

While Woods struggled, 48-year-old Couples turned back the clock to lead fellow veteran Tom Lehman by one stroke with half the field back in the clubhouse.