Pre-tournament favourite Rory McIlroy blamed a "sloppy" short game for an opening round of 74 which left him facing a battle to avoid another early exit from the Irish Open.
McIlroy has a relatively poor record in his national championship, recording two top-10 finishes in seven appearances and missing the cut last year along with Padraig Harrington, Darren Clarke and Graeme McDowell.
The 25-year-old had the added incentives of being able to move top of the European Tour's Race to Dubai and getting back inside the top five on the world rankings with a good performance, but could only finish three over par in perfect conditions at Fota Island.
"I still drove the ball great and got in the positions that you need to, but short-sided myself a couple of times, hit a couple of loose shots with my wedges and could not get a putt to drop," said McIlroy, who had carded an approximate 62 in Wednesday's pro-am.
"I was pretty sloppy with the scoring clubs so I might head to the range this afternoon to work on those. I need to do better tomorrow to be here for the weekend."
Starting from the 10th, McIlroy hit his third shot to the 537-yard par-five over the green and had to scramble for his par, something he was unable to do on the short 11th after finding sand off the tee.
McIlroy split the fairway on the next but had to save par again after coming up short of the green with his approach, while another missed green on the 14th resulted in a second bogey of the day after a duffed chip.
A birdie on the par-five 18th took McIlroy to the turn in one over, but another bogey soon followed on the second when a misjudged approach flew well over the green.
McIlroy was lucky not to pull his tee shot into the water on the third, but failed to make the most of his good fortune before repairing some of the damage with a birdie on the par-five fifth.
After three-putting the sixth and failing to get up and down from a bunker on the seventh, McIlroy at least finished in style with a birdie on the last which prompted the two-time major winner to raise his arms in mock celebration.
"Not being able to do much on Monday and Tuesday was really frustrating, but I played well in the pro-am and had a good practice session on the range till about 8pm last night," added McIlroy, whose clubs only arrived on Wednesday morning after being mislaid in transit from the United States.
"It's tough because I feel like I have been playing well for a while and I am still getting days like this. When you are playing well you should be capitalising on that and not throwing in scores like I did today."
Playing partner Harrington fared considerably better than McIlroy, the three-time major winner also making a birdie on the last to return a two-under-par 69. But that was still five shots off the clubhouse target set by Finland's Mikko Ilonen, who carded eight birdies and one bogey to establish a new course record of 64.
England's Matt Fitzpatrick, who was the leading amateur in last week's US Open, carded a one-over 72 in his first tournament round as a professional.
Ilonen, who lost a play-off to Sergio Garcia for the Qatar Masters in January, had started on the back nine and was three under par at the turn before a bogey on the first proved to be an unlikely catalyst for five birdies in his last seven holes.
"On our 10th hole, the first hole, I made a mess out of it," said Ilonen, who enoyed a three-shot lead over England's Matthew Baldwin and Italy's Edoardo Molinari. "I hit a big drive, middle of the fairway with sand wedge and I walk off with a five.
"Luckily I didn't get too angry with it and I just get going and kept hitting greens and kept giving myself chances. Luckily in the end I made a few putts. I didn't feel so good with the putter today but in the end, it started feeling good."