Spieth becomes second-youngest winner of Masters
Having already set new 36 and 54-hole scoring records, Spieth also equalled the 72-hole record of 18-under set by Tiger Woods in 1997 after a bogey on the 18th, finishing four shots clear of Justin Rose and Phil Mickelson .
Spieth's total of 28 birdies beat the previous best of 25 set by Mickelson in 2001, his last of the week on the 15th also making him the first player ever to reach 19 under par in the Masters.
The 21-year-old is the first player since Ray Floyd in 1976 to lead outright from start to finish, as well as becoming the second youngest champion ever behind Woods.
Now ranked second in the world, Spieth is just five months older than Woods was in 1997, having almost become the youngest ever champion when he led by two shots after seven holes of the final round on his debut last year.
World number one Rory McIlroy, needing to win to complete the career grand slam, had to settle for fourth place on 12 under par after a flawless closing 66, with Japan's Hideki Matsuyama fifth and Paul Casey, Ian Poulter and Dustin Johnson sharing sixth.
"If someone had told me I would finish 12 under at the start of the week I would have taken it and sat back and seen where I finished," McIlroy admitted. "Jordan started fantastically well and has kept his foot down and been really impressive."
Rose twice got within three shots of Spieth on the front nine thanks to birdies on the first and second and bogeys from Spieth on the fifth and seventh, the latter coming after Rose conjured up a remarkable pair after twice tangling with the trees.
Spieth had said after his third round he could not rely on his short game to secure a first green jacket, but an excellent pitch from just short of the eighth green set up a birdie that Rose could not match.
And when Rose three-putted the ninth Spieth had the comfort of a five-shot lead with nine holes to play, with Mickelson another shot back having also bogeyed the ninth.
Spieth took another massive step towards the title with a birdie from 20 feet on the 10th and saved par after a wild tee shot on the 11th to maintain a six-shot lead over Rose and Mickelson - who had also birdied the 10th - with seven holes to play.
A lapse in concentration saw Spieth three-putt the 12th as Mickelson birdied the 13th and the six-shot lead was suddenly down to four.
But Spieth responded with a superb long-iron approach on the 13th and although he missed from 14 feet for eagle, the resulting birdie took him five clear with five holes to play.
Rose closed the gap once more with a birdie on the 14th seconds before Mickelson joined him on 14 under by holing out from a bunker on the 15th for an eagle, the roar causing Spieth to back off his par putt on 14.
However, Spieth responded once more with a birdie on the 15th to become the first player ever to reach 19 under par in the Masters and that effectively made certain of the win.
The star pairing of McIlroy and Woods had failed to produce the early fireworks they needed to get into contention and Woods had more pressing concerns after appearing to hit a hidden tree root when playing his second shot out of the pine straw on the ninth.
"A bone kind of popped out and a joint went out of place but I put it back in," Woods told CBS after just this third appearance of 2015. "Considering where I was after Torrey Pines and Phoenix, to make the complete swing change and rectify all the faults and then come here and contend, I am proud of that."
Woods hit just two fairways in his closing 73, but finishing joint 17th was still a vast improvement on his 82 in Phoenix and withdrawing injured after 11 holes at Torrey Pines.
- PA Sport