Rory McIlroy is the best of Irish on day one of the Northern Trust in New Jersey.
The County Down man hit five birdies, an eagle, and a bogey to finish on six under par alongside Tony Finau, Webb Simpson and Justin Rose.
Troy Merritt has the clubhouse lead, after a flawless round of 62 moved him to nine under par. Dustin Johnson is a shot further back with Jon Rahm and Kevin Kisner both on seven under.
British Open champion Shane Lowry returned to play for the first time since his triumph at Portrush last month. He finished on two under-par, although it might have been better but for a double-bogey six on the fifth hole.
Two late bogeys saw Graeme McDowell drop back to level par.
Elsewhere, Tiger Woods struggled to a four-over-par 75 in the latest indication that all is not well with the 15-times major champion's surgically-fused spine.
He could barely have made a worse start, four over par after nine holes, before somewhat steadying the ship on the back nine at Liberty National.
Since ending a decade-long major drought by winning the Masters four months ago, the 43-year-old Woods has barely played outside the majors and has not impressed when he has competed.