The 24-year-old from Oban had recovered brilliantly from his first double-bogey of the week following a three-putt from close range at the sixth to sit in a tie for ninth with three holes to play in the final round.
Needing to finish in the top 12 to secure an invitation for the 2022 edition, he then dropped shots at the 16th and 17th to find himself in a tie for 17th and needing something special up the last.
Cometh the hour cometh the man. After splitting the fairway with his drive, MacIntyre almost holed out with the approach from 143 yards and showed nerves of steel by rolling in a 13-footer for a birdie.
That left him facing an anxious 20-minute wait to see if his closing 72 for a two-under total would do the job and it was mission accomplished after fellow lefty Brian Harman had to settle for a par at the last.
“Out there I was disappointed with the way I finished, but now I’m delighted,” MacIntyre, who picked up $218,500 for his effort and climbed one spot to 44th in the world rankings, told Sky Sports Golf.
“I’ve got to take the positives and I played great for my first year here. I tried to manage my way round a tough course. I had only played it before on computer games with my pals and it is completely different in the heat of battle.”
He later added: “This is a place you want to be competing every year. My first time this year, and I obviously put up a decent fight, but once you come here, you don't want to miss another one. I'm not missing next year for anything.
“I've played some great golf over the last week, and I feel like my game suits this golf course. The way I play golf suits the way this golf course wants you to play golf. I'm just over the moon to finish the way I finished.”
Asked to pick out his best memory of the week, he replied with a smile: “Holing that putt on 18 to get back next year. I always wanted to play Augusta National, and here we are competing in the Masters, and we're going to do it again next year. This moment right now is everything I've ever dreamed of, and it's what I play golf for.”
MacIntyre, who started out on the final day having made more birdies than anyone else in the field in the first 54 holes, opened with a bogey in the company of Tony Finau.
Continuing to look like a seasoned Masters campaigner on the treacherous greens, he made good pars at the next four holes before having his first blip of the week at the sixth with a double-bogey 5.
His reaction to that bitter disappointment showed he is definitely made of stern stuff, finishing his back nine with birdies at the eighth and ninth before making a brilliant 2 from 10 feet at the 12th then rolling in an 18-footer for another gain at the par-5 15th.
After missing the ridge in the middle of the 16th green, he three-putted from a devilish spot then found trees with his drive at the 17th, but that 72nd hole had the mark of a potential major winner written all over it.
“I am playing against the best in the world and, with a few more rounds, who knows? But I am happy enough with my week,” said MacIntyre.
“If someone had given me tied for 12th for a start, I'd have taken it, but then once I started getting into the battle, I could see how people were making scores.
“Obviously got off to a poor start today, but I battled back the way I normally do. Disappointing bogeys on 16 and 17, but huge birdieing the last.”
The 2015 Scottish Amateur champion was described as a “superstar in the making” by legendary coach Butch Harmon in his Sky Sports Golf commentary on the final day.
This effort came on the back of MacIntyre tying for sixth on his Open debut at Royal Portrush in 2019 before also making the cut as a first-timer in both the US PGA Championship and US Open last year.
He is staying on in the US for one more event - the RBC Heritage at Sea Island in Georgia - before heading home to Oban for a break.
“I'll play next week through the top 50 in the world,” he said. “But I'm going to have a few beers tonight with my family and I'm just going to enjoy it.
“I've got my mom and dad here and the whole team, while I'm sure my two sisters and friends at home will be going mental right now.
“It's part of what we do. We're a big family. We're a close-knit family, and just delighted to be here and competing.”
MacIntyre wore a black ribbon on his hat during the week in memory of Jock MacVicar, the legendary Scottish golf writer and a fellow Argyll & Bute man.
“A legend of a man,” he said. “Great guy, from my neck of the woods, from Dunaverty. Every time he phoned me up we would chat for a good five, ten minutes just chatting about life before we got into golf chat.
“I loved spending time with him, loved chatting to him, and just sadly he passed away. It was a week that I remembered him every step of the way, and that's the reason we wore the ribbon.”