Former FedExCup champion Bill Haas tied his lowest score in a major to snatch the lead at the Masters.
American Haas, whose great uncle Bob Goalby landed the coveted green jacket in 1968, recovered from a bogey five at the opening hole to set the pace on four-under 68.
Adam Scott, bidding to become only the fourth player to win back-to-back Masters, missed only four fairways but failed to make the most of his birdie opportunities on the greens as he returned a 69 to match his effort at the same stage last year.
Bubba Watson shared second place on 69 along with Scott and the player the American left-hander defeated in a playoff here in 2012, South African Louis Oosthuizen.
Rory McIlroy, the 12-1 pre-tournament favourite along with Australian Scott, launched his campaign with a 71.
"Birdying 18 was a huge bonus," Haas, the 2011 FedExCup winner, told reporters at the opening major championship of the year. "I made some nice putts today, a couple of 20-footers, and that can certainly make a difference."