World No 1 Rory McIlroy continued his rich vein of form to be tied for the lead after the opening round of the US PGA Tour playoff event while Tiger Woods lurks a shot behind.

In benign conditions at Crooked Stick Golf Club in Indiana, the elite 70-man field produced a birdie blitz.

Northern Ireland's McIlroy, US Open winner Webb Simpson and his American countryman Bo Van Pelt plus Canada's Graeme DaLaet were the pick of the bunch with equal course-record eight-under-par 64s.

Woods, paired with McIlroy in a mouth-watering shootout, was tied with Vijay Singh just a shot behind the 23-year-old who has won two of his last three starts, including the US PGA Championship and last week's playoff event in Boston. "It was great. With the soft conditions you could really shoot a number out there, and I did," McIlroy said.

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"I took advantage of hitting the ball really well, hitting it in the fairway, which I need to do, and also hitting it long, and gave myself a lot of opportunities.

"I missed a few, but was able to make the most of them. Great start to the tournament."

Adam Scott and Geoff Ogilvy were the leading Australians, staying in touch with four-under 68s to be tied for 16th.

Scott, in need of a top 39 finish to move to the Tour Championship in Atlanta, was left to rue two late bogeys but is still well within the qualification mark and also in contention to win the tournament with three days to play.

The Queenslander made a run at the front-runners with six birdies in his opening 15 holes, including a spectacular hole out from a greenside bunker on the 14th.

But a three-putt bogey on the 16th and another dropped shot on the last when he found deep rough off the tee dropped him four strokes behind the group of four at the top of the leaderboard.

Ogilvy proved he's not ready to give up on the Tour Championship just yet despite facing the daunting task of needing a top-four finish.

It's a position not foreign to the Victorian, as he finished third in the corresponding event last year when a top three was needed.

He started hot with a birdie on the 10th hole but seemed to be treading water with a run of eight straight pars to close his opening nine.

The Victorian then turned on the class on the front side of the course, dropping birdies on the first, second, fifth and seventh holes before his only blemish of the day coming on his last hole.

John Senden is flirting with Tour Championship qualification after a two-under 70 to open his campaign left him tied for 41st to leave him precariously positioned on the projection bubble for the trip to Atlanta in 29th.

Greg Chalmers (74) and Marc Leishman (75), who are chasing top six finishes to advance, will need a huge turnaround over the last three rounds after being two of just 10 players to shoot over par.

- AAP