Storming start from Scott at Masters
Adam Scott of Australia plays a shot during the first round of the 78th Masters Golf Tournament at Augusta National Golf Club on April 10, 2014 in Augusta, Georgia - by Timothy A. Clary
Scott, the defending champion from Australia, was three under at the turn and joint leader out on the course after opening with a birdie and adding two others at the sixth and eighth.
McIlroy, the 2011 US Open and 2012 PGA Champion from Northern Ireland, was playing in the grouping immediately behind Scott and shadowed him all the way with birdies at the third and fifth, but a six at the eighth dropped him back to one-under at the turn.
They were both tucked in, high up an early first-round leaderboard that showed no player tearing up the course despite the perfect playing conditions.
The early clubhouse lead was set at two-under 69 by Jonas Blixt, a 29-year-old unheralded Swede who made it into the Masters by winning last year's Greenbrier Classic, and Kevin Stadler.
Stadler and father Craig, the Masters champion of 1982, earlier became the first father-and-son combination to tee off in the same Masters tournament, albeit in different groupings.
Out on the course, 50-year-old Spaniard Miguel Angel Jimenez was in stunning form to reach the turn at four-under, before dropping one at the 11th, while Brandt Snedeker, who came close to winning here in 2008, was three-under through 10 holes.
Also featuring high up on the fledgling leaderboard were the quiet man of American golf, Steve Stricker, and rising Italian star Matteo Manassero, who both reached the turn at two-under.
Scott, who last year became the first Australian to win the Masters, headed out in the 16th grouping of the day alongside PGA Championship winner Jason Dufner and 19-year-old British amateur Matthew Fitzpatrick.
He is bidding to become just the fourth player to win back-to-back Masters titles after Jack Nicklaus, Nick Faldo and Tiger Woods, the last man to achieve that feat in 2002.
In so doing, he would also take the world number one spot away from the Woods, who is absent through injury.
Eleven minutes later it was McIlroy's turn as he began his bid to win a third major title after the 2011 US Open and 2012 PGA Championship.
The 24-year-old Irishman had for company 20-year-old Jordan Spieth and 23-year-old Patrick Reed -- two rising young US stars on the PGA Tour.
Reed and Spieth are part of a record haul of 24 Masters first-timers who are threatening to turn the game inside out as the generation that spawned such talents as Tiger Woods, Phil Mickelson, Ernie Els and Vijay Singh starts to fade.
Earlier in the morning, the fabled tournament, the first of year's four majors, got underway under clear blue skies, with living legends Nicklaus, Arnold Palmer and Gary Player hitting the first balls as honorary starters.
Golf's famed "Big Three" immediately stepped aside as the action got underway with the first two birdies of the tournament going to 2009 British Open champion Stewart Cink and 1991 Masters winner Ian Woosnam.
If Palmer, Player and Nicklaus were the joint early focus of attention, another legend of the game was missing as, for the first time since he made his Masters debut as a willowy amateur in 1995, the injured Woods was absent.
The four-time Masters winner and holder of 14 major titles announced on April 1 he would not be competing following surgery to repair a pinched nerve in his back that had been troubling him for months.
It was a huge blow for a tournament he has come to symbolize over the last 17 years since his first win in 1997, but players and fans agree that the Masters will always work its magic no matter what.
Even with a fully fit Woods, the tournament would have been as wide open as it has been for years.
Mickelson, who won the British Open at Muirfield last year for his fifth major, was among those expected to be in the hunt come Sunday at Augusta National, where he has won three times previously.
The 43-year-old left-hander, who was doubtful for a while with a pulled muscle in his side, is in the first day's 32nd and penultimate grouping at 1:48 p.m. (1548 GMT) alongside Els and reigning US Open champion Justin Rose of England.
Also among the favorites in a field of 97 was another Australian in the shape of crowd-pleaser Jason Day, who was third last year and tied for second in 2011. He also had a late start.
McIlroy and Rose apart, hopes for a first European Masters winner since Jose Maria Olazabal in 1999 rest mainly with in-form Sergio Garcia of Spain and world number three Henrik Stenson of Sweden.