When the third round began, McIlroy had built a six-stroke lead, the largest lead ever after 36 holes at the Masters.
But after dream rounds - 67 and 65 respectively - during the first two rounds of the year's first golf major, the reigning champion did not have a good Saturday at Augusta National.
Bogey to start
McIlroy bogeyed the first hole. Things got worse on the 11th, when he hit his shot into the water and made a double bogey.
The Northern Irishman wasn't completely out of contention, but after a 73 and 11 under overall, he opened the door to several competitors in the fight for the green jacket.
Scottie Scheffler went out a couple of hours before McIlroy and shot a 65 - the world number one is only four strokes behind the world number two heading into Sunday.
It was also a 65 for American Cameron Young, who shares the lead with McIlroy heading into Sunday.
Sweating in the sun
A handful of other players have the chance to challenge for victory in what promises to be a dramatic finish in the demanding heat of Georgia.
Sam Burns of the USA played with McIlroy on Saturday and narrowed the gap between them from six to one stroke.
Shane Lowry made a hole-in-one at the 6th on the way to a 68, leaving the Irishman two strokes behind the leading duo.
Englishman Justin Rose - three-time runner-up in the Masters - and Australian Jason Day are also in contention, three strokes off the lead.
Ludvig Åberg (tied 21st at -3) and Alex Norén (tied 39th at +1) are, however, too far back to contend despite each shooting a 69 on Saturday.
Rory McIlroy took his long-awaited first Masters victory last year, a triumph that completed a "career grand slam" - victories in all four majors.
Should he defend his title, he will become the fourth player - after Jack Nicklaus, Nick Faldo and Tiger Woods - to win the Masters two years in a row.
