NEWTOWN SQUARE, Pennsylvania - Australian Adam Scott, with tournament host Tiger Woods's regular caddie on his bag, shared the first-round lead at the AT&T National after shooting a four-under-par 66 at Aronimink on Thursday.

Adam Scott of Australia hits off the fairway during the first round of the AT&T National golf tournament at the Aronimink Golf Club in Newtown Square, Pennsylvania, June 30, 2011.  [Photo/Agencies]

Scott made a 15-foot birdie putt at the 18th hole to tie American journeyman Hunter Haas to top the leaderboard after the opening round.

The Australian had a run of three birdies in four holes on his front nine, and Haas moved up the board with four successive birdies on his own front side.

"It's been fun to have (Steve Williams) on the bag for a couple of weeks," Scott told reporters. "I've learned some things. He knows how to manage his way around the golf course. He's got a wealth of knowledge and he's been a great help."

Williams is on loan to Scott with Woods's permission but is expected to return to his long-time employer after the American recovers from his leg injuries and resumes playing.

Woods said this week he has no timetable for his comeback from left knee and Achilles tendon problems. If he can't play in the British Open in two weeks, Scott said he expects Williams to caddie for him at Royal St. George's.

Haas has played most of his golf on the Nationwide Tour over the last five seasons. A former college standout at Oklahoma University, the 34-year-old Haas earned his PGA Tour card for 2011 by finishing third on the Nationwide money list.

Starting his round on the back nine, Haas opened with three pars before a four-hole birdie barrage beginning on the 13th.

Four players were tied for second place on three-under 67, including Jhonattan Vegas of Venezuela and Americans Dean Wilson, Joe Ogilvie and Kyle Stanley.

Wilson, in the first group of the day, holed out for an eagle three at the 558-yard 16th hole on his front nine with a shot out of the deep rough in front of the green.

"It was a pretty decent shot," he said, "but it luckily hit the pin. It probably would have gone about 10 feet by, but it hit the pin and went in."