WORLD NUMBER one Tiger Woods made a shaky start in his quest to remain unbeaten in 2008, posting a level-par 70 in the opening round of the Arnold Palmer Invitational.

Woods, who has won his past five official tournaments - four on the PGA Tour and one on the European Tour - was not at his brilliant best on a pleasant first morning at Bay Hill in Orlando.

But he did enough to stay in touch, five strokes behind early first-round leaders Fred Couples and JJ Henry.

"I just didn't feel comfortable with my irons," said Woods. "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 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 share the lead with Henry. Tom Lehman, and England's Lee Westwood, who dropped a shot at the last, were one shot back. Couples carded six birdies in a five-under-par 65.