Fox missed a birdie chance at three before three dropped shots at five, six and seven saw him five-over through nine.
First, he three-putted the par four fifth hole when his uphill birdie putt was left well short, before a crafty chip with his second shot at the par three sixth was wasted when he couldn’t sink the 3m putt for par. That was followed by another three-putt bogey at the par four seventh, including a miss for par from close range.
Another bogey at the par four 10th after finding the pinestraw with his drive pushed him back to six-over before he shook off the rust at Amen Corner.
He had birdie looks at the 11th, 12th and 13th, but none of them dropped, which could have easily turned his day around.
Eventually, his first birdie of the day came at the par four 17th after his approach from 146m out landed within 3.5m.
Fox sits in a share of 76th with the top 50 and ties making the cut, which currently sits at one-over. He tees off at 3.39am NZT (11.39 EDT) tomorrow.
Burns was the early clubhouse leader including an eagle at the second hole. McIlroy cemented his charge with consecutive birdies at 13, 14 and 15.
Two-time champion Scottie Scheffler is also in the mix after an early eagle at the second.
Masters leaderboard
-5 Sam Burns (F), Rory McIlroy (F).
-3 Kurt Kitayama (F), Jason Day (F), Patrick Reed (F), Justin Rose (9), Scottie Scheffler (7).
-2 Shane Lowry (F), Xander Schauffele (F), Aaron Rai (11), Justin Thomas (8), Gary Woodland (7), Jordan Speith (9).
Other scores: Brooks Koepka Even (9), Cameron Young +1 (F), JJ Spaun +1 (10), Robert MacIntyre +1 (8), Colin Morikawa +2 (F), Bryson DeChambeau +4 (F), Jon Rahm +4 (9).