Tiger Woods, Vijay Singh and Sweden's Henrik Stenson, who got into the field with a win at last year's The Heritage on the European Tour, all shot matching rounds of 4-under-par 66 on Thursday to share the opening-round lead at Firestone Country Club.
Phil Mickelson kept up his strong play from Monday when he captured his second major title at the PGA Championship. He carded a 1-under 69 and is tied for 10th place.
'What I like is I feel very confident with how I'm playing,' said Mickelson. 'I'm trying to take that momentum and carry it over here to Firestone, and the reason I like playing here so much right after last week is it's a very similar setup.'
Woods, who won this tournament from its inception in 1999 through 2001, opened on the back nine and collected his first birdie at the par-3 12th. His 7-iron tee ball hit the flag and rolled back 12 feet, where he holed the putt.
The No. 1 player in the world parred all of his remaining holes on his first side. Woods returned to red figures at the first when his 9-iron approach stopped 20 feet from the hole. He made it two in a row at the par-5 second. Woods' 3-iron second shot missed the green right, but he chipped to 2 feet and converted the short try.
Woods battled some errant drives on the second nine. He saved a pair of nice pars at six and eight, then missed the fairway left at the ninth. Woods knocked a pitching-wedge 15 feet right of the hole and rolled in the birdie putt to grab his piece of the lead.
'I played decent today. I hit some good shots and I also hit some bad ones, but my bad ones weren't really that bad,' said Woods, who tied for second last year behind Stewart Cink. 'All in all, I'm very pleased.'
Woods also continued his fine form from Baltusrol. He opened with a 5-over 75 last week, but fought back with rounds of 69-66-68 and fell two short of Mickelson.
'I felt like I was hitting it well all last week but just didn't putt well,' said Woods. 'I had five three-putts last week, which inevitably ended up costing me probably a chance at winning.'
Singh also posted a top-10 at the PGA Championship and, like Woods, began his first round on the back nine at Firestone. He birdied the par-5 16th, but gave the shot back with a bogey at No. 18.
From there, he went on a birdie run with three in a row from the first. He matched the lead with an 8-foot, downhill birdie putt at the sixth. Singh saved par from off the green at nine to enjoy his share of first place.
'If you drive it good, you can attack the flags,' said Singh. 'I drove it very well on my back nine and hit it close and made the putts.'
Stenson, 29, opened at the 10th and was even for the round when he ran home a 12-footer for birdie at 13. He closed his opening nine with two birdies in his last three holes, both from 8 feet.
His run of impressive play continued at the first when he hit a knockdown 8-iron to 3 feet to set up birdie. Stenson missed the green with his second at the par-5 second, but chipped to 9 feet and rolled in the birdie putt.
At the par-3 fifth, Stenson drained a 65-foot birdie putt and was alone in the lead at 6 under par. He struggled with a bogey at six when he two-putted from 40 feet and fell into a tie for the lead with a bogey at seven after his tee ball found a bunker.
'I know I can play a good game of golf, and I'm just going to try and do that for the next three days,' said Stenson. 'I've had some really good tournaments this year. I've been second twice and third twice, as well. I know I can play well, and I'm just looking forward to the rest of the week.'
Stenson, who is ranked 58th in the world, has one other victory to go along with last year's title at The Heritage. He won the 2001 Benson and Hedges International Open and is 15th on the 2005 European Tour Order of Merit.
Sergio Garcia, Stuart Appleby and Nick O'Hern are knotted in seventh place at 2-under-par 68. Mickelson was joined by Chris Riley and Luke Donald in 10th place at minus-1.
Cink struggled to a 2-over 72 in the opening round of his title defense. He is tied for 32nd place.