Shane Lowry is six shots off the lead after his two-under opening round at the Dubai Duty Free Irish Open, while Rory McIlroy was level par and Padraig Harrington struggled to a four-over 76 at the Mount Juliet course.
Australia's Lucas Herbert leads the way on eight under after a 64 featuring nine birdies and just one bogey.
American Johannes Veerman was a shot behind after a flawless 65.
Scot Grant Forrest is on -6 while 14 players, including Tommy Fleetwood and Martin Kaymer, are a shot further back.
Athlone man Colm Moriarty is the highest-ranked Irishman in the field after a superb four-under 68 that included six birdies.
Lowry was among the first two Irish players on course alongside Northern Ireland's Jonathan Caldwell, with both teeing off from the back nine at 8am.
The 2019 Open champion bogeyed the 13th but bounced back to birdie 15 and 17. A further birdie on two pushed the Offaly native up the leaderboard before a bogey on five stalled his momentum.
However, Lowry bounced back, picking up a shot on the seventh before carding an opening 70, which given the high scoring is just inside the current cut mark.
2016 winner McIlroy looked out of sorts from the off and limped to +2 by the turn with a cold putter.
He did make two birdies and saved par more than once on the back nine however, which gave him cause for optimism tomorrow despite his 72.
"I didn't get off to the greatest of starts... or hole many putts for birdies." Rory McIlroy shared his frustration with @DaveKelly4 after a level-par 72 opening round at the #DDFIrishOpen.— RTEgolf (@RTEgolf) July 1, 2021
⛳ Leaderboard: https://t.co/RRtnLjC8bK
Report: https://t.co/1c08GyrDK4 pic.twitter.com/BX749Sv2ZM
"I feel a bit bad," the world number 10 told RTÉ Sport. "I saved par the last three holes coming in so it could have been worse.
"I didn't got off to the greatest of starts. I didn't feel like I did that much wrong, I just didn't hole many putts for birdies.
"It just sort of one of those days. Overall no momentum going forward. I hung in there and made a couple of birdies on the back nine, which was good, but I felt like the hole looked like a thimble for a few holes and didn't get anything to go.
"Tomorrow morning should be good. We'll get better greens and hopefully I'll shoot a good one."
Australian Lucas Herbert is the clubhouse leader at the Dubai Duty Free Irish Open after an eight-under-par 64.— RTEgolf (@RTEgolf) July 1, 2021
⛳ Leaderboard: https://t.co/RRtnLjkwNa
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Niall Kearney was one shot behind Lowry on one under while Graeme McDowell shot 74.
Lowry's playing partner Caldwell joined Harrington on four over with both players struggling to their opening rounds at the Co Kilkenny course.
Harrington's round included seven bogeys while the three-time major winner birdied the fifth, eighth and 17th.
Paul Dunne opened with a level-par 72, while Cormac Sharvin, Mark Power and Rowan Lester are one shot further back on one over.
Gavin Moynihan is +3 while Simon Thornton is five over after a 77. Caolan Rafferty (+6), Neil O'Briain (+6) and Robin Dawson (+10) bring up the leaderboard.
Watch live coverage of this week's Dubai Duty Free Irish Open on RTÉ2 (Thursday) RTÉ One (Friday-Sunday) and RTÉ Player.