Rahm, making his second start in Europe since joining the European Tour, fired an eight-under 64 in heavy rain at Portstewart to ease to his second worldwide of 2017.
Danny Willett withdrew for the third time in his last five events as he elected to cut short his time at the Dubai Duty Free Irish Open.
Not many people would have tipped the former Walker Cup player to be the leading light from this island come the end of the tournament but it has been a week to confound predictions at every turn. Justin Rose, David Drysdale and Ryan Fox shared fourth.
Rahm shot a second straight 5-under 67 in the third round.
"It's disappointing because I felt like I was playing well coming into the week and I need to do some practice over the weekend and get ready for next week", McIlroy said.More news: Russia, Turkey, Iran to continue talks on Syria de-escalation zones
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Im and Rahm each finished with four pars, meaning there will be nothing to separate the pair - who are separated by 531 places in the world rankings - when the final round begins. He joined Seve Ballesteros, Jose Maria Olazabal and Sergio Garcia on the list of Spanish winners of the Irish Open.
Ultimately, it was all about Rahm, who produced spectacular scoring golf on the final day to continue the 22-year-old's rise as one of the sport's burgeoning talents.
Julien Quesne and Scott Hend both shot 64s for the lowest round of the day and are fifth and sixth, respectively.
The Donegal club have been proactive in tendering for the right to stage one of the European Tour's top events and tabled an official bid in May a year ago where meetings began with European Tour representatives following the Irish Open at the K Club.
Kirk played the first five holes in 1 over with a birdie on No. 1 and bogeys on Nos. On the par-4 18th, she saved par with a 15-footer after finding the right fairway bunker and hitting her approach well left.