Rory McIlroy is best placed of the Irish on one over par.
Shane Lowry endured an up and down opening day on the Oak Hills course for this year's PGA Championship.
The Clara man dropped a pair of shots on his first nine holes.
One of those was retrieved as he birdied the first, his 10th, but another two bogeys came on the way home, leaving the 2019 Open Champion midpack in the field.
Rory McIlroy battled an unspecified illness to card a one over par 71, Padraig Harrington was two over, while Seamus Power was four over par.
Eric Cole has four to play but leads the field on five under.
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