Not since Spieth won the 2015 Masters and US Open has a player won back-to-back majors.
Reed reveled hearing so many prognosticators on Sunday morning pick McIlroy over him.
We take a look at how the final round unfolded at Augusta National.
Reed also got down in two putts from the edge of the green to par the 17th, when his ball raced over the cup, and held his nerve to hole out from three feet for par to triumph at the 18th after rolling his 25-footer past the cup.
Years before his win at the Masters, Reed revealed his boastfulness and said in an interview that he was one of the top players in the world.
The loudest cheers were for everyone else.
Spieth made birdie there, and - with Reed and Rory McIlroy scrambling for pars over the first nine - the tournament was suddenly up for grabs.
He also had two late big slices of luck - firstly on the 13th hole, where he hit his seven-iron approach fat and got lucky when it barely cleared the Rae's Creek tributary and stayed up on the bank. Reed was back where he began at 14 under par, with Spieth breathing down his neck, one shot behind. He is ferocious in match play, especially the team variety, and his singles victory over McIlroy at Hazeltine in the 2016 Ryder Cup led to the nickname of Captain America. Reed is the fourth consecutive Masters champion to capture his first major at that tournament. "I go myself there [this year], I didn't quite do enough", said McIlroy in calm and measured tones, attempting to gloss over the obvious disappointment. "He won't back down".
In 2016 his retail worker sister Hannah shared her side of the family feud on Facebook, calling Reed a "selfish, awful stranger" who "accused me of faking my two kidney surgeries to get him back into my life".
You won't find him on any social media channels during spring break in the Bahamas. "I made too many mistakes". It still wasn't enough.
With a runner-up finish at Augusta National, Rickie Fowler moved up from No. 10 a week ago to No. 6.
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Reed can take the green jacket home with him and is allowed keep it for one year, after which it must be returned to the club.
"I knew the golf course a little better [this year]", he said.
"You had to do it didn't you?"
Given he's never been a unanimously popular player, Reed donning the green jacket prompted a varied and interesting response. "You had to birdie the last".
Had Spieth pulled it off it would have been the greatest comeback in Masters history, but he bogeyed his final hole for a 64 that was one shot off the course record. Asked if his win was bittersweet because he would not be sharing it with them, Reed responded: 'I'm just out here to play golf and try to win tournaments'. It never happened. Never even came close, either.
McIlroy shot 74 and was pretty much irrelevant on the back nine.
The gallery was clearly behind McIlroy, even though Reed led Augusta State to a pair of NCAA titles and briefly lived in Augusta. On the first, where he played pinball with a number of cathedral pines after an errant tee-shot, and again on the fifth and the eighth, his drives went right. "And I had missed it for the last couple of years".
Reed scrambled for a bogey on the opening hole. Mostly, though, it was the putter that let him down as he missed five putts within 10 feet. Reed typically wears red on Sundays in honor of Tiger Woods, who made the look iconic. "Be stubborn", he once said about learning by watching Woods.
Reed was known for his toughness, but that didn't always translate to stroke play. That included Jon Rahm, the 23-year-old from Spain, whose chances ended when he went after the flag on the par-5 15th and came up short in the water. Unbelievably, he was tied with Reed on 14 under. That's all he needed.
"My mindset going in was stick to my game plan, play golf".