Australia's 2013 champion produced a stirring back-nine fightback from two over par at the turn to post an even-par 72 to be just five shots off the early pace.
Scott almost snared a rare albatross before draining an eagle putt on the par-5 13th, only to stumble with two late bogeys including one at the last.
"I wish I would have finished under par today," the 45-year-old former world No.1 said.
"I don't know why that one shot better feels like such a better accomplishment than even (par) but it does, the red number.
"But I'm right there. I didn't shoot myself out of it. That's what majors are kind of all about sometimes. Then you look to take advantage of your good stuff the next few days."
While Jason Day is tied for third at three under, two strokes behind defending champion Rory McIlroy and American Sam Burns, Cameron Smith - like Scott - remains optimistic despite starting with a 74.
Smith also slipped up with bogeys in 17 and 18 after otherwise scrambling superbly all day.
"Kind of scratched it around today," said the former British Open champ who boasts five top-10 finishes from nine previous starts at Augusta National.
"Wasn't my best stuff for sure, I'm definitely not out of the tournament.
"I've left myself with some hard work to do over the next three days, but I've played well round here before."
But Min Woo Lee is certainly out of it after shooting a horror six-over 78.
After racking up five bogeys and a dreaded double on the par-5 13th, when he pulled his drive into the Azaleas, the fan favourite dubbed The Chef conceded he never got cooking.
"Off the tee, I've got to give myself more chances. I didn't hit it really close at all and didn't take advantage of the par-5s. It's a pretty hard recipe to play good without those things," Lee said.
"I take back what I said on Tuesday. I didn't think it was that firm. Now it's like a Saturday firm I would say for a Thursday, which is not really normal.
"It is nearly baked out over those last six holes. It's tough, it's tough."
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