Rory McIlroy fired a three-over-par 74 as he made a disappointing start to his Irish Open bid at Fota Island.
The two-time major winner from Northern Ireland carded six bogeys and three birdies at the County Cork course.
Finn Mikko Ilonen leads after day one on seven under, two shots ahead of German Marcel Siem and Swedes Robert Karlsson and Magnus A Carlsson.
Graeme McDowell is among those on three under, with defending champion Paul Casey and Padraig Harrington two under.
McIlroy ended the first day in a tie for 125th position so the former world number one has much work to do to make the halfway cut.
Pre-tournament favourite McIlroy was in action a day after he announced his intention to play for Ireland at the 2016 Olympic Games in Rio.
The world number six, who started on the 10th, struggled on the greens although he holed from 10 foot for a birdie at his final hole.
His round included four bogeys in six holes from the second while McIlroy also dropped shots at 11 and 14.
"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.
"I was pretty sloppy with the scoring clubs so I might head to the range to work on those. I need to do better tomorrow to be here for the weekend."
Ilonen birdied five of his last seven holes to post an impressive course record 64, setting a tough target for the afternoon starters.
Michael Hoey remains well in contention on three under, with fellow Irish European Tour regulars Gareth Maybin and Shane Lowry on level par.
2011 Open champion Darren Clarke is presently outside the cut mark on one over after opening with a 72.
Sheffield teenager Matthew Fitzpatrick, who was making his professional debut, also posted a 72.
The 19-year-old impressed in his final amateur appearance last week with a top-50 finish in the US Open at Pinehurst.