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.
"I felt like I was battling well, two under through 13, and with another par five coming up, but bogey at the sixth took the wind out of my sails", said McIlroy, who showed his frustration by slamming his driver to the ground after a poor drive at the 16th. He joined Seve Ballesteros, Jose Maria Olazabal and Sergio Garcia on the list of Spanish winners of the Irish Open. Rahm would go on to win the tournament by a whopping six shots. "It's going to be awesome playing with Jon Rahm".
The No. 2-ranked Hideki Matsuyama dropped into a tie for 22nd after a 72.
Changes have been made to the Glashedy course and more will follow as they hope to attract and challenge the best players in the world. Yet the American recovered well to hole back-to-back birdies at the 12th and 13th. Yardage: 7,004. Par: 72.
The biggest news of the day from off the course was the announcement by European Tour chief Keith Pelley that next year's tournament would be held at Ballyliffin on Donegal's Inishowen Peninsula.
Venus Williams at fault in fatal crash; victim's family sues
While Williams was not given a citation by police for the crash, she was found at fault for failing to yield the right of way. Making her 20th career Wimbledon appearance, Williams fought through a spirited first set effort by the 21-year-old Mertens.
The LPGA Tour record for 72 holes is 27 under, set by Annika Sorenstam in the 2001 Standard Register Ping in Phoenix and matched by Sei Young Kim previous year in the Founders Cup, also in Phoenix.
Kirk played the first five holes in 1 over with a birdie on No. 1 and bogeys on Nos.
Sadly, for him, his record lasted only an hour as Scotland's David Drysdale reached -17 with an inspired 63 - rounded off with seven consecutive birdies.
Meanwhile, Im was playing out from the bunker on the par-four 18th.
South Africa's Ashleigh Buhai was second after a 65.