Seven under through 12 holes, Woods carded one birdie, three pars and a pair of bogeys over his final six holes to finish the first round at six under. Woods' 64 on the par-70 Firestone course was good enough to give him a one-shot advantage over Jim Furyk, who shot 65.
Six players are tied for 3rd at four under, including: Darren Clarke, Justin Leonard, Phillip Price, Lee Westwood, Carlos Franco and Phil Mickelson.
Ernie Els is in a 4-way tie for 9th at three under with Stuart Appleby , Loren Roberts and Jose Maria Olazabal.
After successfully defending last week's PGA Championship, Woods began his title defense this week with an eagle three at the par-5 2nd by nearly holing a 6-iron from 206 yards.
Tiger added birdies at the 4th, 5th and 8th - no putts longer than twelve feet - for a front-nine 5-under-par 30; then carded two more red numbers - also birdie putts of twelve feet or less - on the 11th and 12th.
At seven under through twelve holes, Woods was leaving the field in his rearview mirror. However, he slowed down coming home, allowing a host of players to stay within reach.
A six-foot save at the 13th began a run of three straight pars for Tiger, which was ended with his first bogey of the day at the par-5 16th.
Woods' tee shot on the second of the two par fives found the left center of the fairway. From there, Tiger elected to lay-up with a 6-iron. No problem. Woods was just a sand wedge away from the green. Then, inexplicably, Woods flew the green and found the back beach. When he made his way to the bunker, he also found a fried-egg lie.
Tiger's splash out barely made it to the greenside fringe. He two-putted from there for a bogey six.
Tiger regained that lost stroke at the par-4 17th. After catching the rough off the tee, Woods stuck a wedge to six feet. The ensuing birdie moved the 7-time 2000 winner back to seven under par with one hole to play.
Again playing from the rough on the par-4 18th, Woods nearly blew his second shot through a tree. Instead, his ball took a chunk out the tall timber and ricocheted backwards into the fairway.
Tiger's 3rd shot finally found the green. Two putts later, Woods was in the clubhouse signing for his lowest aggregate score since he shot 63 in the second round of the Memorial Tournament - which he won.
Afterwards, Woods went straight to the range to work out some kinks in his driver.
'I didn't drive the ball very well,' said Woods, who hit nine of 14 fairways in the first round. 'I drove it terrible on the back nine.
'I didn't hit the ball very well coming in; and consequently, I didn't shoot the scores I wanted to shoot.'
Fresh off another record-breaking performance at Valhalla Golf Club in Louisville, Kentucky, many wandered if fatigue - mental more than physical - would be an issue this week. Tiger answered those questions in round one.
'I got some rest on Monday and Tuesday, which was nice,' said Woods. 'Came here and played about six holes yesterday, which was nice. And I got a feel of the golf course. Went out today ready to go, and I was able to play well, for the most part.'
Last week, Tiger became the first man since Ben Hogan in 1953 to win three majors in the same season. Woods defeated Bob May in a three-hole playoff to add the Wannamaker trophy to his U.S. Open trophy and the Claret Jug.
This week, no major hardware is on the line, but a million-dollar first-place check is up for grabs. Should Woods prevail again, he would surpass $7.6 million in season earnings.