Seamus Power is three shots off Andrew Landry's lead at the Quicken Loans National, after a first round 66 in Maryland.
Landry and JJ Spaun set the pace in the opening round carding bogey-free rounds of 63, while Waterford native Power made three birdies after teeing off on the back nine, before adding another on his final hole for a flawless opening round.
Also starting on the back nine, Landry made up for a poor round of 81 at last week’s Travelers Championship to finish on seven under.
He was quickly matched by compatriot Spaun, who rattled off five birdies in a seven-hole stretch.
Billy Horschel and Andrew Putnam made up the chasing pack just one shot behind, while Abraham Ancer and Beau Hossler ended on five under.
Tiger Woods, meanwhile, had a disappointing start to the tournament as he was forced to settle for an even-par 70, putting him at joint 48th.
Two birdies helped him recover from a double bogey on the par-4 sixth hole, but he failed to take advantage of several chances despite using a new putter and remained seven shots adrift.
Woods is still attempting to put together the consistency in his game seven months into his comeback from a chronic back injury that required spinal fusion surgery last April.
Last year's Quicken Loans National winner Kyle Stanley could only manage one over par to languish in 68th place.
Collated first round scores in the USPGA Tour Quicken Loans National (USA unless stated, par 70):
63 Andrew Landry, JJ Spaun
64 Andrew Putnam, Billy Horschel
65 Abraham Ancer (Mex), Beau Hossler
66 Joel Dahmen, Ryan Armour, Seamus Power (Irl)
67 Francesco Molinari (Ita), Sam Ryder, Scott Stallings, Brian Gay, Geoff Ogilvy (Aus), Stephan Jaeger (Ger), Ryan Blaum, Marc Leishman (Aus), Cheng-Tsung Pan (Tai), Zac Blair, Anirban Lahiri (Ind)
68 Roberto Diaz (Mex), Stewart Cink, David Lingmerth (Swe), Lanto Griffin, Fabian Gomez (Arg), Jamie Lovemark, Bronson Burgoon, Tom Hoge, Joaquin Niemann (Chi), Ollie Schniederjans, Patrick Rodgers, Troy Merritt
69 Adam Schenk, Nick Watney, Jason Kokrak, Benjamin Silverman (Can), Byeong-Hun Ant (Kor), Gary Woodland, Adam Hadwin (Can), Ethan Tracy, Billy Hurley III, Derek Fathauer, Denny McCarthy, James Hahn, Cameron Percy (Aus), Tyler Duncan, Corey Conners (Can)
70 Scott Brown, Tiger Woods, Robert Garrigus, Ryan Palmer, Dylan Meyer, Svn Woo Kim (Kor), Charles Howell III, Doc Redman (a), Ben Crane, Martin Laird (Sco), Kevin Tway, Rickie Fowler, Dominic Bozzelli, Kevin Nam, Aaron Baddeley (Aus), Michael Thompson, Kiradech Aphibarnrat (Tha), John Huh, Blayne Barber, Johnson Wagner
71 David Hearn (Can), Kelly Kraft, Cody Gribble, Robert Streb, Richy Werenski, Tom Lovelady, Chad Campbell, Xinjun Zhang (Chn), Tyrone Van Aswegen (Rsa), JT Poston, Chris Stroud, Kyle Stanley, Andrew Yun, Chesson Hadley, Matt Every, Alex Cejka (Ger), Jonas Blixt (Swe), J.J. Henry, Whee Kim (Kor), Rob Oppenheim, Keith Mitchell
72 Brian Stuard, Rory Sabbatini (Rsa), Martin Flores, Matt Jones (Aus), Sung Kang (Kor), Nicholas Lindheim, Harris English, Kevin Streelman, Ted Potter, Jr., Bill Haas, Michael Kim, Jonathan Randolph, Nick Taylor (Can)
73 Peter Malnati, Shawn Stefani, Harold Varner III, Tim Herron, Doug Ghim (a), Kristoffer Ventura (Nor), D.A. Points, Danny Lee (Nzl), J.B. Holmes, Brandon Harkins
74 Ricky Barnes, Trey Mullinax, Talor Gooch, Rod Pampling (Aus), Jimmy Walker, Jason Gore
75 Sam Saunders, Daniel Summerhays
78 Martin Piller