Masters and US Open champion Jordan Spieth is one off the lead on 5-under par.
There's a five-way tie on 6-under, with Retief Goosen and 1999 champion Paul Lawrie among those heading the field.
A fine opening round of 69 will see Greystones amateur Paul Dunne end the first day of the Open Championship on 3-under par.
A quadruple bogey 8 at the 17th scuppered Shane Lowry's fight back – he dropped from 3-under to end the day on 1-over.
Darren Clarke is 1-under, Graeme McDowell is level.
While Padraig Harrington has parred the first.
