Knox carded a four-over-par 76, a three-shot improvement on the corresponding day on his debut at Augusta National 12 months ago.
He was out in level-par 36 before dropping four shots coming home, the bulk of the damage being caused by a double-bogey 6 at the 14th.
“I played well, but was just untidy,” reported the 31-year-old afterwards. “My mum could have got up and down from some of the positions I failed to today.”
He’d started well in that department by producing a good par save at the first before doing likewise at the third after holing from around five feet for a birdie - his only one of the day - at the second.
“On the back nine, I was just off the edge at the 11th, but didn’t get up and down,” added Knox.
“Then, at the 14th after my second shot was just tugged a bit and kicked on hard into the straw, I thought I’d played a great chip, but it came up just short.
“I made a mess of it from there and that was two shots gone. I flagged it at the last but just went off the back, from where I failed to get up and down again.”
It left Knox sitting joint-57th, leaving him with work to do in his bid to be here for the weekend.
“My iron play was pretty good. I felt I hit a lot of solid shots. It was just tough to get it close enough to make birdies,” he continued.
“I felt that two or three-over would be par today. I should have got it round in par, so that is disappointing.”
He reckoned that conditions had contributed. “That’s about as hard as you will play in. It’s not just the wind. It’s the slopes on the greens and how fast they are,” he said.
“They said it was going to gust up to 40mph - and I believe them as I almost fell over on 14!
“We play in wind a lot. The tough thing about here is all the trees. You don’t really know where it is.
“At least when you are playing somewhere like Troon you know where it is. Here it is tricky. You can’t pick your club until it is your turn to hit.”
Makking his 36th appearance in the event, Sandy Lyle was also out in level-par before having to settle for a 77 after he had “frittered away” shots on the back nine.
“I played very good for the first nine,” said the 1988 champion. “I thought I would get through Amen Corner and maybe birdie 13 I would be one under or level and very happy.
“But I hit some sloppy tee shots and was out of position a few times.I took a penalty on 13 because I was out of position in the azaleas on the left - I hardly ever go there.
“I was then blocked out on 14 and made 6. And on 16 I put it back of the green on the right, which you just don’t do.”
Sitting in a share of 66th, Lyle has a battle on his hands to avoid a third successive early exit.
“You are just hanging in there,” said the 59-year-old of the conditions. “You have to be so accurate with your landing areas, so you get a bit negative.”