Padraig Harrington impressed in the opening round of the Travelers Championship in Connecticut with a four-under-par round of 66, while Bubba Watson leads on eight under.
The Dubliner, who carded five birdies and one bogey, is tied for 15th on a crowded leaderboard with four players on six under and nine just a shot further back.
Watson’s round included nine birdies and one bogey.
Americans Keegan Bradley, Brian Stuard, Harris English and Seung-Yul Noh of Korea are all two shots behind the 2012 and 2014 Masters champions.
Watson was driving the ball an average of just over 325 yards on Thursday and he admitted that his distance was proving a big help around TPC River Highlands.
"If I drive it halfway decent, I'm going to have short irons, I'm going to have wedges," he told Sky Sports 4.
"I think we counted up around five holes that aren't wedges so that means if my wedges are halfway decent I'm going to have a lot of birdie putts."
Bradley recorded seven birdies and a single bogey on his way round and the 2011 US PGA champion admitted that playing on lush greens compared to the highly-criticised surfaces at the US Open at Chambers Bay last week made a big difference.
"I made some real good putts on the back, which was my front side, that kind of kept it going," he said.
"Coming from last week to this week, the greens are perfect any week but especially coming from last week, it seems so easy to make putts. If you feel like you get it on line, it's going to go in."
Meawhile, Waterford’s Seamus Power leads the way after the first round at the Air Capital Classic in Kansas on the buy.com tour, the level below the PGA Tour.
He recorded a seven-under round of 63.
