Woods was perched atop the leaderboard with Sweden's Freddie Jacobson, Spain's Sergio Garcia, Northern Ireland's Graeme McDowell and American Bubba Watson, the defending Masters champion.
Phil Mickelson was one of four players a stroke behind the leaders as the elite field took advantage of easy scoring conditions.
The Blue Monster course at Doral was once considered a beast but has become a toothless resort course over the years, tamed by equipment changes as players deal comfortably with the lengths.
Owner Donald Trump has ordered the bulldozers in after this tournament to begin a massive rebuilding project, which is aimed at making the course far more challenging.
On Thursday, though, bathed in sunshine with little wind and temperatures relatively cool for South Florida, the course offered a generous farewell party with only 16 players shooting over-par.
The world's top three players - McIlroy, Woods and England's Luke Donald - were grouped together, providing a fascinating opportunity to compare their games with the US Masters just over a month away.
Woods's nine birdies were his best tally since the opening round of the BMW Championship last September, while McIlroy shot a one-over 73 after racking up six bogeys.
Woods has won this tournament on six occasions at various venues, including most recently in 2007 at Doral where he also won the Ford Open twice.
Starting on the 10th hole, the 14-times Major winner followed two birdies with bogeys at the 13th and 14th holes before quickly bouncing back by picking up shots at the 16th and 18th.
"It was certainly a day that could have been a little bit lower," said Woods. "This is probably the easiest wind we'll have, some of the hardest holes were playing downwind, and it really wasn't blowing that hard most of the day."
McIlroy was still working through his swing troubles and found just three fairways and 11 greens.
The 23-year-old Northern Irishman was making his first start since walking off the course midway through his round at last week's Honda Classic at PGA National in Palm Beach Gardens.
He picked up two shots with an eagle on the first hole, his 10th, but looked far from the player who won five titles last season, including his second Major.
"It was a bit of a struggle to be honest," said McIlroy.
"Hit some good shots, hit some not-so-good shots. As I've been saying all week, this is a work in progress and I'm working at it and I'm staying patient.
"I've got another three rounds here to try and work on it a bit more and shoot a few good scores and we'll see what happens."
Woods, by contrast, was solid in all aspects of his game and impressive with his putter, the highlight being a birdie putt from 38 feet on the fourth hole.
The world number two had spent time on Wednesday with his friend Steve Stricker, working on his putting and it clearly paid off.
Stricker himself was just one shot off the lead along with compatriots Mickelson, Hunter Mahan and Swede Peter Hanson.
Defending champion Justin Rose of England was one of six players two strokes back along with compatriot Ian Poulter after shooting a 68.
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