The Masters 2016: Rollercoaster Rory McIlroy battles as champ Jordan Spieth sets pace
Rory McIlroy showed Jordan Spieth that the defending champion is not going to have it all his own way in the 80th Masters at Augusta.
While the American powered to a stunning six under par 66, the Ulsterman is two under after a promising 70.
McIlroy signalled his intentions to become only the sixth player in history to complete the career Grand Slam with a superb eagle on the 13th to move to three under par and pushed on from there to move to four under with a birdie at 15. But bogeys at 16 and 18 followed.
McIlroy's fellow Ulsterman Graeme McDowell is on the fringes of contention after a level par 72.
McDowell was satisfied with his round.
"All in all, in the blustery conditions - the wind was tough - you had to pick your moments. I am happy with level par," said the Portrush native.
Defending champion Spieth assumed his customary position on top of the leaderboard with a brilliant 66.
Spieth, who was second on his debut in 2014 and claimed a first Green Jacket with a record-breaking performance 12 months ago, carded six birdies and no bogeys despite swirling winds on the opening day at Augusta National.
The 22-year-old, who is looking to become just the fourth player after Jack Nicklaus, Nick Faldo and Tiger Woods to successfully defend the year's first Major championship, led from start to finish after an opening 64 last year and was quickly into his stride with birdies on the third, sixth and eighth to move into the outright lead.
Another birdie on the 10th was followed by crucial par saves from the trees on the 11th and over the green on the 12th, before the US Open champion two-putted the 13th for birdie.
Spieth, who set records for the highest number of birdies (28) and lowest 36 and 54-hole totals in Masters history last year, understandably kissed his putter in delight after holing from 15 feet for par on the 16th.
And the world number two then finished in style with a birdie from five feet on the last to reach 29 under par for his nine competitive rounds at the Masters.
Assuming he is not overtaken, his leaderboard position after each of those rounds will read 12-3-1-2-1-1-1-1-1.
At six under par, Spieth led by three shots from playing partner Paul Casey, who carded six birdies and three bogeys in his 69, with last year's joint runner-up Justin Rose also three under with four holes to play.
Two-time Masters champion Bubba Watson was alongside Rose after birdies on the first, seventh and eighth, with world number one Jason Day also three under thanks to an eagle from 10 feet on the second and a birdie on the fifth. Day finished level.
Irishman Shane Lowry (left) was in joint second after picking up a hat-trick of birdies from the second, although the WGC-Bridgestone Invitational champion was among the later starters due to face winds gusting between 30 and 35mph.
But the Offaly man coped with the conditions superbly to finish four under par.
"I started nicely and that settled me down. Then I was off and running. I am pretty happy. It was difficult - it was windy," said Lowry.
Ian Poulter is bang in contention after a three under par 69.
"That was tricky out there," he said. "I wanted to take care of all the par fives. The wind was swirling around the front nine, but I played lovely.
"I had two three putts for the day, that's a little frustrating because if I hadn't then I'd be even closer.
"But it has been good start - probably one of my best starts at the Masters."
First man out, Jim Herman, had a good start after securing the last place in the 89-man field by winning last week's Houston Open.
However, he then carded a hat-trick of bogeys from the fourth and signed for a 75.
World number five Rickie Fowler fared even worse despite recovering from a double-bogey on the first with birdies on the second, third and fifth, the 27-year-old running up a triple-bogey eight on the 13th and a double bogey on the 16th in an opening 80.