The 24-year-old from Oban had the leaders in his sights after covering the first 10 holes at The Renaissance Club in five-under-par, having birdied the third, fifth, seventh, eighth and 10th to move to 10-under.
But, after missing from four feet in taking a bogey at the par-3 14th, he then had to settle for an even more disappointing par at the 16th, where he had an eagle putt but then missed from no more than two feet for his birdie.
“I’m raging right now, to be honest with you,” said MacIntyre after signing for a four-under 67 - his best round of the week - to sit on nine-under. “It was a disappointing finish.
“I was right back in the golf tournament and now I feel as if I’m right back out of it just with a couple of putts. But that’s golf, isn’t it?”
The Scottish No 1 reckons he’s not been the same from close range since missing a two-foot putt at the eighth hole at Emirates Golf Club in the final round when in contention in the Omega Dubai Desert Classic earlier this year.
“Up until Dubai, I never felt I missed a putt inside six feet,” he added. “But, ever since I missed that wee putt in Dubai, I feel as if I’ve missed more putts inside six feet than I ever have.
“I don’t know what it is. I’m working at it and feel good over it and then I hit it and it gets halfway and it’s missing. Just need to get back and work at it.
My problem right now is I hit it too hard. It just doesn’t feel smooth. I used to be silky smooth with the short ones, dropping them in dead weight. Just now it just isn’t perfect.”
MacIntyre, who is currently the sole Scot in the field for next week’s 149th Open at Royal St George’s, had a 12-under-par total in his sights before seeing some of his earlier good work undone slightly.
“Early on, it was easy golf,” said the 2019 European Tour Rookie of the Year. “I was knocking it onto par-5s in two and driving the green at the par-4s. It wasn’t as if I was hitting great shots to make things happen, it was just so simple.
“I was trying to get the 12 and it felt easy to do that. I hadn’t missed a shot and I was driving it a lot better. I’m disappointed with the finish and I’m absolutely raging right now.”
Connor Syme carded a 69 to sit on six-under, two better than Grant Forrest after three dropped shots in two holes left him having to settle for a 72.
Calum Hill, the sixth Scot to make it to the weekend, missed a 54-hole cut after a 76, which included a triple-bogey 8 at the seventh, left him on three-over.