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.

Gibraltar FA Latest To Pull Its Support For Gianni Infantino
Fulham And Chelsea Face Off In A West London Derby Tonight
Troy Parrott To Make Real Betis Debut Tomorrow
Monday Morning Sports Update
Weekend SFC, IFC, JFC C'hip Results
Athlone Town Reach Fifth Straight FAI Women's CUp Final
All Blacks Strike First In Springboks Rugby Test Series
McIlroy Strides Into Contention At BMW Championship Despite Rocky Second Round