Seamus Power stormed out of the blocks with an opening 66 to share 12th place after the opening round of the AT&T Byron Nelson in sweltering Texas.
The West Waterford star (31) missed just two fairways at Trinity Forest Golf Club in Dallas, rattling in six birdies in a five-under-par round to lie five shots behind leader Marc Leishman, who shot an immaculate 10-under 61 to lead by three strokes from JJ Spaun and Jimmy Walker.
Sam Saunders, Aaron Wise, Keith Mitchell, Abraham Ancer, Jonathan Byrd, Ethan Tracy, Jonathan Byrd, Tyler Duncan and JT Vogel carded six-under 65s with Graeme McDowell outgunning playing partner Jordan Spieth by two as he fired an eagle and four birdies in a four-under 67 to share 23rd spot.
McDowell was criticised on social media for taking his time over a tricky up and down on the 17th but he had no problem explaining himself to some fans as the players sometimes struggled to make up their minds on a new and exciting course
Pádraig Harrington made six birdies but was left to rue four bogeys in a two under par 69 that leaves him just inside the projected cut line after a 69
On the Challenge Tour, there was also a 66 for Derry's Ruaidhri McGee, who is just two shots off the lead after a six-under opening round in the Andalucía Costa del Sol Match Play 9 in Spain.
Welshman Stuart Manley leads the race to make the top 64 who will contest the nine-hole matchplay knockout series tomorrow after he shot a seven-under 64 at Valle Romano Golf to lead by a shot from England's Matt Ford and Austria's Markus Habler.
McGee (27) made an eagle two and five birdies in his 66 to share fourth place on a mixed day for the Irish.
Ballymena's Dermot McElroy is tied for 15th after a three-under 68 with Ardglass' Cormac Sharvin and Galgorm Castle's Michael Hoey tied 27th after 69s.
But it was a struggle for last year's runner-up Gavin Moynihan, who won the recent GolfSixes with Paul Dunne but is in danger of missing his 11th cut in a row after opening with a 73.
Whitehead's John Ross Galbraith and Clendeboye's Jonny Caldwell are four shots outside the projected cut after three-over 74s while West Waterford's Gary Hurley signed for a six over 78.
On the European Tour, Belgium's Thomas Detry delighted the home fans as he produced a big finish to share a seven-way tie for the lead in the Belgian Knockout
He birdied the last three holes at Rinkven International Golf Club to shoot a four-under 67 and share top spot with English pair Matthew Baldwin and Ryan Evans, Spain's Jorge Campillo, Chile's Nico Geyger, Malaysia's Gavin Green and Dane Jeff Winther.
The top 64 after today's second round will advance to a nine-hole stroke play knockout with the winner being crowned on Sunday after a total of 90 holes.