“Any time you can shoot three under around this place you have to be happy,” said McIlroy, who is well aware that his record as a professional on home soil leaves a lot to be desired.
“The conditions were pretty tough early on and then the wind seemed to settle a little bit those last few holes and it was nice to take advantage of that and play them the way I did.
“Giving those shots away on 14 and 15, to get more than both of them back on the last three holes was a great way to finish and gives me plenty of momentum going into Friday morning.
“It’s nice to get off to a good start in Northern Ireland for a change. I enjoyed being out there, the crowds were great.
“Really pleased with how I started and hopefully I can continue into the next three days.”
Denmark’s Soren Kjeldsen won a three-man play-off to lift the title in 2015 and was just a shot behind McIlroy on two under after a superb 69.
The 49-year-old is preparing for life on the seniors tour next year, but could sign off in style with a fifth European tour title.
Former Open champion Shane Lowry had to settle for a one-over-par 72, but that represented a good effort after dropping shots on the second and third and then missing the fourth green.
There was little to cheer for the Australian challengers with Jason Scrivener lying joint-101st after an opening 74 while David Micheluzzi ended a miserable outing in the cold and wind with a quadruple-bogey nine at the 18th that left him clutching a horrible card of 79.
Irish Open leaders
1: Todd Clements -5
2: Alejandro Del Rey -4
2: Sami Valimaki -4
4: Will Enefer -3
4: Filippo Celli -3
4: Rory McIlroy -3
4: Thriston Lawrence -3
4: Marcus Armitage -3
