The 2009 champion signed for a three-under par round of 69.
Shane Lowry is leading the home challenge after his opening round at the Irish Open at The K Club.
The 2009 champion signed for a three-under par round of 69, and is three shots off the clubhouse leader, Nacho Elvira.
Rory McIlroy is two shots further back, alongside Brooks Koepka on one-under.
The reigning Masters champion was frustrated after his group was put on the clock midway through his opening round:
In the afternoon groups today, Seamus Power is up to two-under.

Alcaraz Withdraws From Wimbledon Due To Wrist Injury
Graeme McDowell To Make His First Major Appearance In Six Years Next Month
Three Of The Irish Provinces To Kick Off The New Season At Home In September
Tuesday Morning Sports Update
All Ireland Football Championship Opening Round Fixtures Confirmed
Tommy O'Brien Among Injury Doubts For Leinster's Champion Cup Final On Saturday
Monday Morning Sports Update
Sunday Evening Sports Update