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Jordan Spieth holds a two-shot lead going into Friday's second round after carding a six-under-par 66 at Augusta National.
With Rory McIlroy slipping back late to two under, Spieth made his move early with three birdies on the front nine.
The 22-year-old American added three more on the back nine as he went through his round without a bogey.
"I put it up there with one of the best rounds I've played," said world number two Spieth. "I got a lot out of the round with what I felt like was kind of average-ish ball striking."
After a stellar 2015, Spieth came to Augusta in less certain form.
But his remarkable record on this course - runner-up to Bubba Watson on his debut in 2014, champion in a record-equalling score a year ago having made a first-round 64 - continued as greens softened by overnight rain did only a little to compensate for a tricky blustery wind.
A birdie on the 10th was followed by crucial par saves from the trees on the 11th and over the green on the 12th, before a two-putt on the 13th for birdie.
Spieth, who is looking to become just the fourth player after Jack Nicklaus, Nick Faldo and Tiger Woods to retain the Masters title, kissed his putter after holing from 15 feet for par on the 16th.
And he finished with a birdie from five feet to reach a cumulative 29 under par for his nine competitive rounds at Augusta.
"I think the round may have been better than the first round last year because of the conditions - I would have signed for two under today and not even played the round, knowing the conditions that were coming up," said the Texan.
Casey said of his playing partner: "That was a flawless round. I played a wonderful round, but it was great to have a front-row seat to watch that."
World number one Jason Day had moved to within a shot of Spieth on the 14th but then three-putted the 15th before driving into the water on 16.
That resulted in a double bogey and a four-shot swing across the two holes, and an errant tee shot on the next led to another dropped shot as he closed on even par.
Lowry, 29, had four birdies across the first five holes and held on across a solid back nine to join New Zealand's Danny Lee on four under.
"I'm sure I'm going to be sitting back tonight thinking at some stage about wearing a Green Jacket. I'm only human," he said.
"But I've just got to kind of give myself a slap in the face and get myself back into reality and try to get down to business and keep hitting good shots and see where that leaves me at the end of the week."
After a contrastingly inconsistent start, McIlroy began his own charge with an eagle on the 13th, a magnificent approach followed by a 10-foot putt.
A birdie attempt on the next missed by a whisker, but he sank a 12-foot putt up the slope on 15 to go to four under, only to miss a short one on 16 to drop back.
He then put a short approach on the 18th into the bunker, splashed his shot from the sand 20 feet past the flag and left the par putt short to end the day in 10th.
"If someone had given me 70 on the first tee I probably would have taken it," said McIlroy. "It's a little disappointing with the way I finished, but anything under par was a good score."
Casey, who finished joint sixth last year after failing to qualify for the previous two Masters, had moved within a shot of the lead with a birdie of his own on the 16th before dropping back with a bogey on the par-four 17th.
The 38-year-old was joined at three under by first Rose, in a round that combined six birdies with three bogies, and later an upbeat Poulter.
Rose, joint second a year ago, was utilising a new putting grip, switching to a 'claw' for the first time.
"I stumbled across it last week and it just felt too good to deny," said the 35-year-old.
"I have putted OK this year but I feel if I am going to win the Masters I am going to have to putt great - it was a gamble but I felt it was one worth taking."
Poulter, 40, dropped shots on 10 and 11 but battled back with birdies on the 13th, 14th and 16th.
He said: "That was tricky out there - the wind was swirling around the front nine, but I played lovely."
Four bogeys and a double bogey on the back nine left two-time champion Watson with a three-over 75, but it was South African Ernie Els who was the talk of the course after a horrific putting display on the first green.
The four-time major winner, who has twice finished second at the Masters, reached the green in three but then six-putted from within three feet.
It was the worst ever first-hole score at the tournament, and left the 46-year-old five over as he trudged to the second tee.
Rickie Fowler was another big name to endure a poor start as a double bogey on the first and an eight on 13 contributed to an eight-over-par 80.
"Golf's tough. It's a fine line, especially at this place," the American said.