Three-time major winner Brooks Koepka and fellow American Bryson DeChambeau share the lead at the Masters after carding rounds of six-under 66 on the first day.
Five-time major winner Phil Mickelson finished with five birdies in seven for a five-under 67 - his lowest opening round since he won in 2010.
England's Ian Poulter and US hope Dustin Johnson were four under, while five players including Australia's Adam Scott and Spaniard Jon Rahm were a shot further back. Tiger Woods was one of 10 players at two under.
Koepka, 28, who sat out last year's Masters with a wrist injury, had four straight birdies between the 12th and 15th holes but missed a birdie putt on the 18th for the outright lead.
DeChambeau birdied the last four holes and six of the last seven.
Scott's best opening round at the Masters in five years had the 2013 Augusta National champion sitting on three-under-par 69.
He had not broken par at the April major since the 2014 edition but birdied the final two holes and briefly shared the clubhouse lead with South Africa's Justin Harding and Rahm.
Scott was treading water at even par through 14 holes but surged up the leaderboard to two under courtesy of birdies at the par-5 15th, the difficult par-4 17th and the last hole.
Australian Jason Day finished a shot back at two-under.