Graeme McDowell leads the Irish challenge heading into the second day of the AT&T Pebble Beach Pro-Am in California.
The Ulster man, playing at Pebble Beach where he won the US Open in 2010, lies three shots off the lead following a four-under par opening round of 68.
Shane Lowry is one-under.
The American pair of Brian Gay and Scott Langley share the top of the leaderboard.
Gay produced an impressive birdie run to take a share of the first-round lead at the AT&T Pebble Beach Pro-Am in California.
The American got to five under at the turn thanks to five straight birdies from the fifth on the Monterey Peninsula course and had just one blemish on the back nine to fire a seven-under-par 64.
Countryman Langley, starting on the back nine, birdied half his holes on the same course, including one on the par-three ninth, to join Gay at the top of the leaderboard.
Five-time major champion Phil Mickelson sits one shot off the lead after making five birdies on the back nine for a 65 as he hit every fairway in a PGA Tour round for the first time since 1998.
He was matched by former world number one Jason Day, who had just one bogey on the par-four 15th before recovering with three birdies in a row.
The tournament is played over three courses - Monterey, Pebble Beach and Spyglass Hill - before the final round at Pebble Beach on Sunday.
Englishman Tommy Fleetwood finished two over after a triple-bogey on the 13th at Monterey, while Ryder Cup team-mate Paul Casey mixed four birdies and a bogey at Pebble Beach to card a 69.