Padraig Harrington started the day in joint-second and ended up missing the cut following a cataclysmic second round at the Irish Open on Friday.
Overnight leader Ryan Fox, Matthieu Pavon and Erik van Rooyen share the halfway lead.
New Zealand's Fox, son of All Blacks World Cup-winning flyhalf Grant, sank three birdies on the back nine to card a three-under-par 69 and take the clubhouse lead at eight under
He was joined by Frenchman Pavon after a second consecutive 68 while South African Van Rooyen left it late, finishing with back-to-back birdies in a course-record 65 to make it a three-way tie atop the leaderboard.
Sweden's Joakim Lagergren carded a 68 to finish one shot behind the trio at Ballyliffin Golf Club and one ahead of a group of players including Britain's former US Masters champion Danny Willett.
It was a day to forget for Harrington though.
The Dubliner had been quoted by some bookies as being as long as 66/1 to triumph in Donegal this weekend, a price that Harrington himself said was "good value".
But following a strong start on Thursday which left him on four-under-par, a shot behind New Zealand's Ryan Fox, he crumbled.
Wayward driving plagued the 46-year-old's game all day and a rollercoaster back nine me managed two double bogeys - one on the 18th which sealed his fate - two birdies and a bogey.
Added to the three bogeys he notched on the front nine, it meant Harrington signed off with a six-over 78 to end his tournament on two-over.
Rory McIlroy was left to rue dropped shots at the end of his second round but took solace in at least making the cut.
The Northern Irishman won at the K Club in 2016 but didn't qualify for the weekend in the other four of the last five years. The former World No 1 shot a one-over-par 73.
"It's a change," he told RTÉ Sport. "It's a success in terms of the last few years so it's nice to play the weekend.
"I didn't play quite as well as yesterday but I still had chances to make birdies.
"(I got) three. I bogeyed three of the last five, which isn't great.
"I played okay. I had a couple of loose tee-shots coming in and they cost me a couple of bogeys late on but the game felt ok."
.@ShaneLowrygolf feels he played well in his #IrishOpen second round and was happy to avoid another "smelly finish". pic.twitter.com/1X54chhxB8
— RTEgolf (@RTEgolf) July 6, 2018
Former Irish Open winner Shane Lowry fared better, shooting four birdies and two bogeys in a 70 that moved him to two under overall.
Paul Dunne squeaked in just under the cut mark with a 72 but Gavin Moynihan suffered the opposite fate after a second successive one-over 73.
Former Ryder Cup captain Paul McGinley (+3) and Darren Clarke (+4) both also miss out.
Lagergren added a 68 to his opening-day 69 to move into the outright lead.
Danny Willett is one shot behind him after a 70 - the Englishman reached a career-high of ninth in the world after claiming his first major title at Augusta National in 2016, but has slumped to 442nd in the rankings after suffering numerous injuries and a loss of form. He is joined by South African Zander Lombard.
Lee Westwood, who will be one of Thomas Bjorn's vice-captains in Paris in September, was a shot further back following a 71.
Four-time major winner McIlroy isn't giving up hope of a title tilt just yet but admits he needs a good round tomorrow to have any chance of contention.
"It's getting firm and fast out there.
"One of the guys that shot four or five under yesterday might shoot another good one today and get to eight or nine but I can't really worry about that.
"I've just to worry about myself, go out tomorrow and try to shoot a good one and get myself in the tournament."
McIlroy has had little success with the putter so far this week, and a shot that lipped out on the 18th (his ninth) seemed to encapsulate his struggles.
"It sort of sums up the last couple of days," he said. "Even the good ones aren't going in.
"I didn't hole anything again on the greens but hopefully I can turn that around over the weekend."
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