AUGUSTA, 7 Apr 2016, (AFP) - The Texan, just 21 at the time, was the first wire-to-wire winner in 40 years at Augusta National last year, and his bogey-free opener brought up the possibility he could do so again as he led by two strokes at the end of the first round.
Only Jack Nicklaus, Nick Faldo and Tiger Woods have managed back-to-back wins in the Masters.
Spieth was the only player in the 89-strong field not to cough up a bogey on a breezy day in the first of the year's four majors.
The American, who opened with an eight-under 64 en route to his record-matching victory last year, reached the turn in 31 after birdies at the fourth, sixth and eighth and he added three others down the back nine at 10, 13 and 18.
Taking advantage of fine early playing conditions as the 80th Masters got underway, Spieth was in the clubhouse and able to sit back and see if top rivals Jason Day and Rory McIlroy could keep pace with him during the afternoon's action.
They could not.
His day's best means that he has been the leader after six of the nine Masters rounds he has played at Augusta National since his debut in 2014, including the last five in a row.
"I feel like my game has been trending in the right direction, I just haven't gotten scores out of how I felt I'd been playing," said Spieth.
"That normally just comes down to putting. Certainly made a lot of putts today. If I can kind of straighten things out with the iron play, hopefully we'll be in business.
"But, yeah, I am extremely pleased with that round today. I felt like we stole a few."
Underlining the quality of Spieth's round was the fact that only seven other players were able to score in the 60s.
Adopted New Zealander Danny Lee got closest after a 68, 13 strokes better than in the last round he played at Augusta as an amateur in 2009, and he was joined at 4-under by fast-improving Irishman Shane Lowry.
A stroke further back were three Englishmen -- Paul Casey, Justin Rose and Ian Poulter -- alongside Spain's Sergio Garcia and Soren Kjeldsen of Denmark.
Career Grand Slam seeker McIlroy could have joined them on that mark, but he plugged his approach to the last in a bunker and took a bogey as a punishment.
"One of the toughest days I've ever seen around Augusta National," Casey said of the windy playing conditions. "I was impressed by everything (Spieth did) today. That was a flawless round of golf."
It was an odd round for world number one Day, the tournament favorite who is aiming for back-to-back major titles after taking the PGA Championship last year.
He charged out in 5-under 31 but then limped back in at 5-over 41 to end where he started at level par.
"Obviously it's frustrating, but I am not too disappointed because I thought I played well in general," he said. "Even if I gave up five shots in three holes I am only six back after one round."
McIlroy, with four majors under his belt already, eagled the 15th to get to 4-under but promptly three-putted to hand one back and then bogeyed the last to fall to 2-under.
"I am a little disappointed the way I finished, but 70 was not a bad score out there and in the 60s would have been really good," he said.
Three-time former winner Phil Mickelson came in with a level 72, but 2013 winner Adam Scott struggled all day for a 76 as did Bubba Watson for a 75.
There were struggles, too, for another top American hope, Rickie Fowler, who was moving along smoothly at even par through nine, but then bogeyed 10 and took an eight at the par-5 13th, where he hit into Rae's Creek in front of the green.
Fowler went into the water again at the 16th for a double bogey and finally limped in with an 80, leaving him with a mountain to climb just to make the cut.
"Golf's tough. It's a fine line, especially at this place," a crestfallen Fowler said.
But that was nothing compared to the horrors that beset four-time major winner Ernie Els, who had an astonishing nine at the par-4 first hole, virtually wrecking his tournament in the space of a few minutes.
It was the worst-ever score at the opening hole in the history of the tournament.
Golf legend Tom Watson, playing his 43rd and final Masters at the age of 66, impressed with a 74 that left him in with an outside chance of making the cut for the weekend.
"I'm still there. I think 74 is not bad for old folks," the two-time Masters champion said
First round scores in the Masters at par-72 Augusta National on Thursday:
66 - Jordan Spieth (USA)
68 - Danny Lee (NZL), Shane Lowry (IRL)
69 - Sergio García (ESP), Soren Kjeldsen (DEN), Paul Casey (ENG), Justin Rose (ENG), Ian Poulter (ENG)
70 - Danny Willett (ENG), Rory McIlroy (NIR), Billy Horschel (USA), Scott Piercy (USA)
71 - Kevin Streelman (USA), Jimmy Walker (USA), Charley Hoffman (USA), Brandt Snedeker (USA), Emiliano Grillo (ARG), Hideki Matsuyama (JPN), Lee Westwood (ENG), Matthew Fitzpatrick (ENG)
72 - Chris Wood (ENG), Graeme McDowell (NIR), Henrik Stenson (SWE), Bernhard Langer (GER), Louis Oosthuizen (RSA), Jason Day (AUS), Phil Mickelson (USA), J.B. Holmes (USA), Thongchai Jaidee (THA), Kiradech Aphibarnrat (THA), Zach Johnson (USA), Bryson DeChambeau (USA), Kevin Na (USA)
73 - Brooks Koepka (USA), Davis Love (USA), Dustin Johnson (USA), Daniel Berger (USA), Smylie Kaufman (USA), Hunter Mahan (USA), Angel Cabrera (ARG), Bernd Wiesberger (AUT), Victor Dubuisson (FRA)
74 - Romain Langasque (FRA), Rafael Cabrera (ESP), Marc Leishman (AUS), Cameron Smith (AUS), Martin Kaymer (GER), Harris English (USA), Troy Merritt (USA), Vaughn Taylor (USA), Tom Watson (USA), Keegan Bradley (USA), Jamie Donaldson (WAL)
75 - Jim Herman (USA), Bubba Watson (USA), Matt Kuchar (USA), Bill Haas (USA), Branden Grace (RSA)
76 - Charl Schwartzel (RSA), Anirban Lahiri (IND), Adam Scott (AUS), Mike Weir (CAN), Derek Bard (USA), Patrick Reed (USA), Justin Thomas (USA), Chris Kirk (USA), Larry Mize (USA), Jason Dufner (USA), Darren Clarke (NIR), Sandy Lyle (SCO)
77 - Webb Simpson (USA), Fabián Gómez (ARG), Trevor Immelman (RSA), An Byeong-Hun (KOR), Kevin Kisner (USA), Mark O'Meara (USA)
79 - David Lingmerth (SWE), Steven Bowditch (AUS), Jin Cheng (CHN), Russell Knox (SCO)
80 - Andy Sullivan (ENG), Vijay Singh (FIJ), Ernie Els (RSA), Rickie Fowler (USA), Ryan Moore (USA)
81 - Robert Streb (USA), Sammy Schmitz (USA)
82 - Ian Woosnam (WAL)
83 - Paul Chaplet (CRC)