Seamus Power hit five birdies in his opening round of the Travelers Championship to sit just two shots off the leaders in Connecticut.
The Waterford native began his challenge on the back nine in Cromwell and made two birdies inside the first four hole, but also dropped a shot in between the two gained stokes.
Power proceeded to shoot a flawless front nine with three birdies on the second, third and seventh holes to post four under and sit two shots off a group of six players heading into the second round.
Padraig Harrington is also in the field on the east coast of America and the three-time major winner enjoyed a solid start, shooting two under par in his opening round.
PGA Tour rookie Lee Kyoung-hoon of South Korea used a hot start and two back-nine birdies to move into that leading group on six under par.
Lee, who missed the cut at last week's US Open, went out in the afternoon at TPC River Highlands and birdied four of the first six holes and then added another two at the 13th and 17th for a career-low, six-under-par 64.
The bogey-free trip around the course left Lee level with Mexico's Abraham Ancer, Canada's Mackenzie Hughes and Americans Ryan Armour, Bronson Burgoon and Zack Sucher.
England's Paul Casey arrived at the par-four 18th in a share of the lead but failed to hit the green with his approach and then settled for a closing bogey after missing a 16-foot par putt that left him in a group of six players one shot back.
Patrick Cantlay was also cruising along with a chance to grab the outright lead until a bad swing at his penultimate hole ultimately left him two strokes behind the leaders.
Cantlay, who won the Memorial Tournament less than three weeks ago, started on the back nine and was tied for the lead before a double-bogey at the par-three eighth where his tee shot found the water in front of the green.
The American, who has eight top-10 finishes in 15 events played this season, closed with a par for a four-under-par 66 that left him in a share of 13th place.
"Just hit it a little fat, and it's got to get up in the air to get the wind," Cantlay said of his tee shot at eight.
"It was downwind and didn't get the wind because I hit it fat and it went in the water."
Norwegian Viktor Hovland, who was the low amateur at last week's US Open, shot a three-under-par 67 in his professional debut to sit tied for 25th.
Tournament favourite Brooks Koepka, fresh off a runner-up finish at the year's third major, mixed four bogeys with three birdies for a one-over-par 71 while defending champion Bubba Watson (69) was five shots behind the leaders.