McIlroy, who was a late entry into the £3m (€3.42m) event after failing to qualify for the Tour Championship, carded a three-under-par 67 to lie four shots behind leaders Tyrrell Hatton and George Coetzee at Close House.
However, it could have been a different story for the four-time major winner if a spectator had not found his ball inside the five-minute time limit after a wild drive on the 17th, his eighth hole of the day.
McIlroy produced a superb recovery from thick rough to the elevated green and went on to make three birdies on the front nine in his penultimate tournament of an injury-plagued season, which the former world number one will bring to an early end after next week’s Alfred Dunhill Links Championship.
“It’s not a bad way to feel,” said the 28-year-old. “You’re not really looking ahead at anything, you’re just concentrating on the round out there and not thinking about anything else.
“I feel like I’m not under any pressure to perform at all, I’m not putting myself under any pressure. That’s probably the reason I’ve went out there and shot a decent score.
“I think if you asked 75% of the guys out here, they would say it would be nice to have some sort of an off-season.
“I’m just giving myself an off-season this year and looking forward to improving my health, improving my game and becoming a better player in 2018.”
Speaking about the 17th, McIlroy admitted he feared a repeat of the final round in this year’s Open at Royal Birkdale, when a wild drive on the 15th resulted in a lost ball.
“I thought it was going to be the Open all over again,” he added. “I’ve hit a few destructive tee shots like that over the past few weeks just by going for it. I was trying to get it to the front of the green and I was in two minds whether to hit it at that point or not, because the guys in front were still on the green. I thought I’ll just say sorry if it gets close to them.”
Hatton had not made a halfway cut since May, before finishing third in the Omega European Masters three weeks ago, a run of form he puts down to listening to “too many opinions” about his swing.
“I’m not a tech person and there were a few numbers being thrown around which I didn’t want to know,” said Hatton after a brilliant back nine of 30, which included a bogey on the 11th.
“My swing feels good now and I’ve got a good friend, Jonathan Bell, on the bag and we’re just trying to have a bit of fun. He’s a pro himself and wanted to play on the EuroPro Tour this year, but didn’t have the funds.
“He’ll work for me until the end of the season and, hopefully, that will give him a great platform for next year.”
Wicklow man Paul Dunne impressed on his way to a 66, as did Antrim’s Graeme McDowell, while Offaly’s Shane Lowry carded a solid 68.
Lee Slattery, who made worldwide news when he watched his wife give birth to their second child via FaceTime while he competed in Switzerland, carded five birdies in a flawless 65 compiled alongside 16-year-old amateur Robin Tiger Williams.
Williams, who was born in the year that Tiger Woods completed the ‘Tiger Slam’ of holding all four major titles at once, carded a respectable 71 and said: “It was so fun and enjoyable. I had trouble getting to sleep on Wednesday night and I was definitely nervous on the first tee, but as I got into the round I settled down and handled it very well.”
Tournament host Lee Westwood, Martin Kaymer, Matt Fitzpatrick, and Ian Poulter all shot 66, but Masters champion Sergio Garcia had to settle for a level-par 70. Defending champion Alex Noren finished one over.