The race to catch clubhouse leaders, Ryan Fox, Matthieu Pavon and Erik Van Rooven began early at Ballyliffin on Saturday morning.
Among the early starters were Portrush's Graeme McDowell who had started the day in joint 51st position on level par.
He soon found his rhythm and made birdies on the par four third and par three fifth. But a bogey on nine saw him turn at one under.
A bogey on 11 had him back at par.
Rory McIlroy who finished one-under for his first two rounds, made a terrific start with a birdie at the first, but he was back at one under by the second with a bogey on the par four.
Defending champion Jon Rahm made four birdies in the first five holes to put him right in serious contention.
The leaders are due to tee off at around 1pm.
McDowell looked to be heading for a level round, but he bogeyed his last to leave him one over for the day.
England's Andy Sullivan came in with a seven under 65 to support the thoughts the Glashedy Links did have a big score on it and set the early clubhouse target on six under overall.
Rahm began the third round seven shots off the lead shared by Ryan Fox, Matthieu Pavon and Erik van Rooyen, but slashed his deficit to just two thanks to a brilliant front nine of 30.
The world number five birdied four of the first five holes and recovered from a bogey on the seventh by holing from 30 feet across the green on the next for another birdie.
And the 23-year-old then made the most of a slice of luck on the ninth, where his approach to the green took a favourable bounce off the slope of a bunker and set up a sixth birdie of the day from five feet.
Rahm was on five under by the 15th hole, His round to that point included six birdies with a bogey on seven his only blemish on the front nine.
It was another mixed bag for McIlroy having opeedn with a birdie he had a bogey on the second and although he had birdies on four and six, a bogey on seven and nine took him into the turn level par. He parred the 10th and 11th.
Ireland's Paul Dunne, one of the early starters, finished level par for the day and one over for the tournament.
Rain began to come in for the final groupings heading out of the course and it was interesting to see how that could impact on the scores.
Rahm's charge ground to a halt on the back nine and the Spaniard's frustration was summed up when his birdie attempt on the 18th caught the edge of the hole and span out.
"Oh, you've got to be kidding me," Rahm said as he had to settle for nine pars in succession and a third round of 67 to join Sullivan in the clubhouse lead on six under.
That was four off the overall lead held by Van Rooyen, the South African making the ideal start in pursuit of a first European Tour title with birdies on the first and second.
Rahm, who won by six shots at Portstewart last year, said: "I played about as flawless a front nine as I can play. The only bad moment came on seven when my club got stuck a little bit on the ground and missed the ball left of the bunker.
"I wish I would have hit more fairways on 10 through 15, although with the wind being different it was a little harder to hit some fairways.
"It's frustrating because I played extremely good and I felt like I could have gone a lot lower, but let's just hope tomorrow will be a better day."
McIlroy was also frustrated to bogey the last and card a third round of 72 which ended his chances of winning the title for the second time in his final year as tournament host.
"It's tough," McIlroy said. "On this golf course it feels like you should go out and shoot five or six under par every day, but it's a little trickier than that and it's tough walking off the course even par when you've given yourself loads of chances.
"I felt if I had shot something in the 68, 67 range I'd have given myself a decent chance tomorrow but I'll just try to round off the week with a good round tomorrow."
In contrast, Van Rooyen showed no signs of struggling on the greens and birdied the fourth, seventh, eighth and ninth to race to the turn in 29 and enjoy a four-shot lead over Sweden's Joakim Lagergren.
Shane Lowry was left disappointed as he came in two over on the day - bogeying the last hole - to leave him level for the weekend.
Van Rooyen was unable to find any further birdies on the back nine, but a bogey-free 66 gave the 28-year-old a total of 14 under par and a four-shot lead over Fox and Lagergren.
Former Masters champion Danny Willett was a shot further back after recovering from a poor start with five birdies in seven holes from the 11th, with Scotland's Russell Knox six off the lead on eight under.