The world number one, seeking his fifth title at the Bay Hill Club, rattled up seven birdies and one bogey in relatively calm conditions to finish level with fellow American Vaughn Taylor and Briton Paul Casey.
Play was suspended for the day at 1830 local time (2330 GMT) because of the threat of lightning with 11 players still out on the course.
Spaniard Sergio Garcia fired a five-birdie 66, his lowest round on the 2007 PGA Tour, to lie two strokes off the pace with Sweden's Carl Pettersson, Trevor Immelman of South Africa and Americans Rocco Mediate and Sean O'Hair.
South Korea's K.J. Choi and American Mark Calcavecchia, winner of last week's Tampa Bay Championship, were among a group of 10 players bunched on 67.
Bay Hill specialist Woods, back on the Tour after a two-week break, was in upbeat mood after a polished display at one of his favourite venues.
"It's definitely my best round of the year," the 31-year-old told reporters after hitting 17 greens in regulation. "I hit the ball well and felt like I controlled my flight all day, even when the wind started picking up.
"I missed a couple of putts early on but after that I felt I rolled the ball really well. We had the benign conditions early and I just wanted to go out there and shoot at least under par on that front nine.
"I may have left one or two (shots) out there but 64 around here is not too bad."
Woods, who won the Buick Invitational in his first start of the season, said he had not played as well from tee to green since last year's WGC-American
"I did it pretty good at the Amex, and I did it for all 72 holes there which was fun," he added, referring to his eight-shot victory at The Grove in Hertfordshire, England last October.
After teeing off at the par-four 10th, Woods reeled off four birdies in five holes from the 11th, a 28-footer at the par-four 15th lifting him to four under.
He ran up his only bogey of the day at the par-four 18th, his wedge approach spinning back off the front of the green to finish beside rocks guarding the water from where he had to take a penalty drop.
Out in three-under 32, he picked up further shots at the third and seventh before hitting a superb approach to within seven feet of the flag at the ninth.
Taylor, a double winner on the PGA Tour, carded six birdies in a blemish-free display to set the early pace with Woods before they were joined by Englishman Casey, who signed off with a birdie at the difficult par-four 18th.
"It's the best start to a tournament I've had so far this year," said Casey, who won his eighth European Tour title at the Abu Dhabi Championship in January.
"I struck the ball really well, got a little stale in the middle and then to birdie the last was fantastic."
Ernie Els, winner at Bay Hill in 1998, opened with a 69 while Masters champion Phil Mickelson dropped five shots on his way to a 72.