Coming off his win last week in Massachusetts, Rory McIlroy fired an 8-under 64 on Thursday to grab a share of the lead after the opening round of the BMW Championship.

The PGA Champion was joined atop the leaderboard by U.S. Open winner Webb Simpson, Bo Van Pelt and Graham DeLaet.

Tiger Woods, who was paired with McIlroy, carded a 7-under 65 and is tied for fifth with Vijay Singh at Crooked Stick Golf Club.

Luke Donald, Ryan Palmer and Ryan Moore share seventh place at minus-6.

Part of the reason for the low scores was that players were playing under lift-clean-and-place rules due to a very wet course. Rain from Hurricane Isaac soaked the course last weekend and more rain fell on Wednesday.

McIlroy posted back-to-back 67s on Sunday and Monday to win the Deutsche Bank Championship. That helped him increase his lead atop the world rankings and gave him momentum entering this week.

The 23-year-old opened with a birdie on the 10th, but he gave that shot back when he bogeyed the par-3 13th. An eagle on the 15th and a birdie at 18 helped McIlroy make the turn at minus-3.

He made it two in a row with a birdie on the first. McIlroy's roll slowed as he had one birdie and five pars between the second and seventh.

McIlroy birdied the eighth to get within one of the lead. He pitched his third to four feet at the par-5 ninth and rolled that putt in for birdie.

"You know, with the soft conditions you could really shoot a number out there, and I did. 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," said McIlroy. "I missed a few, but was able to make the most of them. Great start to the tournament."

Simpson and Van Pelt played alongside one another and were hot from the start. Van Pelt birdied three of the first four holes to jump up the leaderboard. Simpson had just one birdie, to go with six pars, in the first seven holes.

Van Pelt moved to 4-under with a birdie on the seventh. Simpson caught fire with a birdies at eight and nine. He also birdied the 11th to get to 4-under. Van Pelt ran off three birdies in a 4-hole span from the ninth to climb to minus-7.

After the duo both parred the 13th, Simpson flew into contention as he poured in four consecutive birdie efforts from the 14th to grab the lead at minus-8.

Van Pelt birdied the last to join him there.

DeLaet started on the back nine and he carded three birdies in a row from the 11th. After stumbling to a bogey on the 16th, he birdied each of the next four holes to move to 6-under. DeLaet parred six straight before rolling in a 34- footer for eagle at the ninth, his last, to join the lead.

Woods flew out of the gate with birdies on three of his first four holes. He stumbled to a bogey at the 14th, but came right back with birdies at 15 and 16 to get to 4-under.

Around the turn, Woods birdied the first and second. A poor drive on the fourth led to another bogey. He erased that mistake with a birdie on No. 5, then chipped in for birdie at the ninth to finish one behind the leaders.

"I was scoring. I wasn't playing particularly well, but I scored. Rory on the other hand played beautifully today. Every single part of his game was working," Woods said in a televised interview with McIlroy. "It all looked good. I was very fortunate to post the number I shot."

NOTES: Defending champion Justin Rose opened with a 5-under 67 and is tied for 10th with five others...With bad weather in the forecast on Friday, tee times were moved up to 8:00 - 10:01 a.m. ET...Four players have finished in the top 10 at the first two playoff events - Brandt Snedeker, Dustin Johnson, Louis Oosthuizen and Kevin Stadler.