Unheralded Charley Hoffman takes a four-shot lead into Friday's Masters second round after high winds punished the world's top golfers and favorite Dustin Johnson withdrew injured.
Hoffman, 40, posted a seven-under par 65 in conditions described by one former Masters winner as 'borderline' unplayable.
He snatched the lead over second-placed fellow American William McGirt on a day of high drama that saw world number one Johnson pull out following a freak accident.
Hoffman's four-stroke lead is the largest at the Masters after 18 holes since 1955, when Jack Burke led by the same margin over Julius Boros.
In the difficult conditions, Hoffman said he set out to shoot for par but "got a little bit lucky."
"For lack of any better words, it was a dream," he said.
England's Lee Westwood, 43, still looking for a major title after 75 attempts, was in third place a shot further back on 70 on a day when top contenders suffered in difficult conditions on the 7,435-yard Augusta National course.
Johnson agonized for 24 hours before pulling out after a serious fall on the eve of the tournament left him in pain from a lower back injury.
"I wanted to try and play but I'm not going to be able to compete," he said. "It just sucks."
Reigning US Open champion Johnson had been the oddsmakers' favorite in the year's first major golf championship after winning his three prior starts but hurt himself in a fall down stairs Wednesday at a rental house.
Without the world number one, Northern Ireland's second-ranked Rory McIlroy and Australian world number three Jason Day were tipped to be key contenders for the title.
However, neither had it their own way in the opening round.
Nor did another top contender, former Masters champion Jordon Spieth, who suffered a repeat of last year's quadruple-bogey disaster.
- Beyond tough -
The 2013 Masters champion, Adam Scott of Australia, said the conditions were beyond tough.
"It's very difficult conditions and borderline (unplayable)," he said after returning a three-over 75.
Steady but swirling winds above 20 mph (32 kph) with gusts twice that speed sending tee shots and approaches soaring off target and even kept balls rolling on greens.
Four-time major champion McIlroy appeared to be struggling in the wind and was three-over after the front nine.
He opened with a bogey on the first hole and dropped shots on the third and fifth to make the turn in 39. But on the way back he sank three birdies to salvage a 72 and a share of 12th place.
"My short game really saved me today -- 10, 11 and 12 -- to get up and down was huge," he said.
"Even par was a pretty great score out there at the end of the day and I'm happy with it."
McIlroy was one shot behind England's 2013 US Open champion Justin Rose, who was in an eight-way tie for fourth on 71.
Day also suffered in the conditions, returning a two-over 74 with a double-bogey on the 11th hole to share 26th place.
For 2015 Masters champion Spieth, the day turned sour on the back nine in a near repeat of the quadruple-bogey nightmare that cost him back-to-back titles last year.
The American, twice a Masters runner-up, had been five shots ahead on the final day last year before he imploded after taking seven shots on the par-3 12th.
This time out, he negotiated the 12th hole in regulation but took a nine on the par-5 15th, ballooning his score before sinking a birdie at 16 to limit the damage to finish on 3-over 75.
- 'I need to snag something' -
Spieth said the quadruple-bogey blowout put him under pressure for the following three days.
"I feel like I need to snag something tomorrow," he said.
One man who thrived in the conditions was three-time former Masters champion Phil Mickelson, who fired a 71 for a share of fourth place.
"Man, I love it," Mickelson said. "I thought anything at par or better was going to be a great score and it is."
The 46-year-old US left-hander will replace Jack Nicklaus as the oldest winner in Masters history if he can collect a fourth green jacket on Sunday.