The straight-hitting Englishman, who has yet to win a taylormade r11 driver sale
, fired a five-under-par 67 at a rain-softened Augusta National where tough pin positions posed all sorts of problems for the game's leading players.
Westwood birdied the par-four 17th, then parred the difficult 18th to edge one ahead of South African Louis Oosthuizen, who stormed up the leaderboard with four birdies in the last five holes, and ice-cool Swede Peter Hanson.
Pony-tailed Spaniard Miguel Angel Jimenez, Italy's Francesco Molinari, Britain's Paul Lawrie, Americans Ben Crane, Bubba Watson and Jason Dufner carded 69s while tournament favourite Tiger Woods eked out a level-par 72 after bogeying 17 and 18.
Westwood, who finished second here in 2010 when he also opened with a 67, was delighted with his strong start in the year's first major.
"There was no weakness out there today in my game. I hit it close, hit a lot of fairways and rolled in some nice putts," said the 38-year-old, who has six times finished in the top three at majors.
"When this golf course is soft, it obviously gives you a bit more of a chance, but I think they were slightly worried about the scoring getting out of control, so they tucked a lot of the flags away.
"You can play your taylor made r11 driver
out of a tournament in the first round, and I haven't done that, so I'm right where I want to be and looking forward to the next three days."
Oosthuizen, who romped to a seven-stroke victory in the 2010 British Open, steadily worked his way up the leaderboard after making a slow start before ending his round with a 20-foot birdie putt at the 18th.