To win last year, McIlroy needed to beat Justin Rose – who finished tied third on Sunday having led by two at the turn – in a sudden death play-off after bogeying the 72nd hole.
And he did not make it much easier for himself this time around. Having scorched the field to take a record six-shot lead after 36 holes, he stuttered to a one-over 73 on Saturday.
Tied with Young going into Sunday, Northern Ireland’s McIlroy heaped pressure on himself with a sloppy double-bogey five on the fourth after three-putting from eight feet.
He dropped another shot at the par-three sixth, but after mixing four birdies with seven pars to build a two-shot lead over world number one Scheffler heading to the last, he said his “greatest stress” on Sunday was not knowing where his ball ended up on the 18th after flailing his drive right and in among the trees.
“It could go anywhere. It could be anywhere,” added the world number two, who also drew level with Americans Phil Mickelson and Lee Trevino on six majors.
“There were a few others. I thought my second putt on 11 was huge to avoid making bogey there.”
Despite falling behind Young and Rose, and with Scheffler creeping up the leaderboard, McIlroy insisted he never felt as though his chance had slipped away.
“If I hadn’t birdied the seventh and eighth holes, I would have started to push a little bit,” added the 36-year-old, who became just the sixth wire-to-wire Masters winner.
“But I think the birdies on seven and eight, Justin bogeying 11 and 12, and then me birdieing 12, I never felt like I was out of it. I never felt like I had to press at all.”