Pieters dropped a shot on the first hole but the other three safely negotiated the difficult par-four and world number eight Fowler and Hoffman birdied the second to move to five under.
Spaniard Jon Rahm and fellow competitor Fred Couples, the 57-year-old American former Masters champion, picked up birdies at the par-five second hole to get to two under and Rahm rolled in another smooth putt at the third.
American William McGirt also birdied the second to join Rahm and Pieters at three under.
World number two Rory McIlroy, the highest-ranked player in the field following the withdrawal of Dustin Johnson, made a move with two early birdies but a double-bogey at the seventh dropped him back to two over.
Three-times Masters champion Phil Mickelson birdied the first two holes but a double-bogey at the third put the experienced American left-hander on level par.
It was a miserable start for four-times major champion Ernie Els, who is seeking his first Masters title at the age of 47.
The South African made a double-bogey and five bogeys in his first eight holes to slump to 10 over par. (Editing by Andrew Both)