Jason Dufner, the PGA champion, made a 9 on the par-5 13th en route to an 80. Phil Mickelson, who won the Open Championship last year, made a triple-bogey 7 at the seventh and doubled the par-5 15th after hitting his third into the water. He shot 76. Justin Rose, the reigning U.S. Open winner, shot 76.
Scott got to the top of the leaderboard with a birdie at the 10th, his fourth of the day. But his tee shot at the par-3 12th with a 9-iron from 158 yards came up woefully short, landing on the bank and bounding back into the water.
That led to a double-bogey 5 that knocked him from the top of the leaderboard, but he bounced back with a birdie at the 14th. And although he had three-putt pars on the 13th and 15th holes, Scott was pleased with the first round of his title defense.
"I was really very happy with the way I played today tee to green," Scott said. "It was really how you hope to come out and play at any major, and especially the Masters. I was really solid."
Haas, who won the PGA Tour's FedEx Cup three years ago, has five PGA Tour titles but has never finished among the top 10 in a major championship, his best a tie for 12th at the 2011 PGA Championship.
After a bogey at the first, he birdied the second, fourth and eighth holes, added birdies at the 13th and 14th holes, dropped a shot at the 17th but got it back on No. 18 to post a score that would hold up as the first-round lead.
The bad news for Haas is that of the 77 previous winners of the Masters, only nine had the outright first-round lead. In fact, there have been 283 stroke-play majors since the first Masters was held and only 8.5 percent of their winners led after the first round.