The four-time major victor, who needs to win the Masters to complete the career grand slam, hit a superb pitch to three feet but missed the par putt to leave himself five shots off the lead.
McIlroy was six shots off the lead overnight after a frustrating third-round 71, and he admitted he needed "the round of my life" to have any chance of becoming the sixth player to complete a career grand slam of majors. "It's heightened even more, just because you can hear what's going on around you", McIlroy said about the roars and groans of Augusta's massive galleries.
"I've shown myself many times after that I can contend and I truly feel I cannot only win one (major) but more than one".
At the par-five second, the 27-year-old reached the green in two to set up an early birdie and he followed up with another at the short par-four third, chipping to two feet.
McIlroy then drove just short of the green on the short par-four third and chipped to two feet for another birdie, before leaving his hat-trick attempt short from 18 feet on the next. "I'll be able to tell you better tomorrow night whether those missed opportunities hurt my chances".
Two closing pars kept him at three under for the tournament, and he said: "It wasn't quite as adventurous as previous Masters have been for me".
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If I'm still in Los Angeles , I will nearly certainly go to the game, since it would be just a four hour drive away. Raiders games will continue to be played at the Oakland Coliseum in 2017 and likely 2018.
"It's just a stat", said the 25-year-old Belgian, who won four of his five matches at Hazeltine.
If McIlroy can get off to that quick start, he may put a little pressure on the guys playing behind him as he tries to chase them down.
Adam Scott, the 2013 champion lies in seventh on three under following a 69 with 2011 victor Charl Schwartzel eighth on two under thanks to a third-round 68, one ahead of European Ryder Cup stars Lee Westwood and Thomas Pieters. But I gave a decent account for myself and will come back next year and try again. "But I'll move on and focus my attention on the US Open".
"Oh, I just didn't want Jeff to beat me", said the Australian. He hit a first-round 65 in 2011 and a final-round 66 in 2015.
There was trouble ahead though, a bogey at the par-four fifth and double bogey seven at the seventh to undo his strong opening, althugh he reclaimed a short with a birdie at the eighth. McIlroy's ball took a bad bounce right and into the trees, and then he made matters worse by getting "cute" with his greenside-bunker shot.
As the talented Augusta member who is frequently relied upon to tee it up over the weekend when an odd number make the cut, Knox has gained a degree of notoriety - particularly after he apparently shot a better score than Rory McIlroy when the duo were paired together in 2014.