Shane Lowry and Seamus Power both put in impressive opening rounds at the AT&T Pebble Beach Pro-Am and are currently just four shots off the clubhouse lead.
The Irish pair both carded contrasting rounds of 70 in California, while Pádraig Harrington found the going tougher, but a late flourish saw the three-time major winner settle for two-over-par 72.
The Irish trio were among the earlier finishers, with Americans Rick Lamb and Joel Dahmen, along with South Korea’s Seung-Yul Noh, leading the way at four-under-par.
Lowry and Power both birdied the first, with the Clara man picking up three birdies and dropping three more by time he reached the 11th.
From there he sparked into life and birdied four of the following five holes.
A dropped shot on the final hole, the 543 yard par five, saw him finish level with Power who made most of his headway on the front nine, picking up shots at the first, second and seventh holes.
Harrington struggled from the outset and was three-over-par at the turn, but birdies at 15 and 18 saw him finish the day two-over-par.
Jordan Spieth also finds himself in early contention after a rain-affected first round.
Spieth is one of four of the world's top 10 who are hoping to avoid being upstaged by their celebrity partners in California and he made the best start, placed at three under when the inclement weather halted his round after 16 holes.
That leaves him a shot off the lead, shared by Rick Lamb, Seung-Yul Noh and Joel Dahmen, when his first round concludes on Friday.
Spieth fired six birdies and two bogeys in treacherous conditions on the Monterrey Peninsular Country Club and will hope to lay the foundations of a first PGA Tour win since May 2016.
World number one Jason Day went round the same course in two-under-par 69 while Dustin Johnson is one under with two holes left to play.
Justin Rose is also on one under with six holes to play as much of the field are forced to finish their first rounds on Friday.
Each player and their celebrity partner plays one round at Pebble Beach, Spyglass Hill and Monterrey Peninsular Country Club over the first three days, with the leading 25 pro-am teams and top 60 professionals and ties returning for the final round at Pebble Beach on Sunday.
