Kuchar finished the day three shots back with a 69 and would have been a worthy champion, the 39-year-old American playing some magficiant golf of his own.
The win marks Spieth's third major championship, putting him in one elite class. Spieth now joins the "Golden Bear" Jack Nicklaus as among the only golfers to win three parts of the grand slam before turning 24 years old.
To cut a long story short, Spieth carded a miracle bogey on 13, a birdie and nearly an ace on 14, an eagle on 15, a birdie on 16 and another on 17 to win by three.
Japan's world number two Hideki Matsuyama and Branden Grace of South Africa are both four-under with the latter fresh from becoming the first player ever to shoot a round of 62 in a major championship on Saturday.
- Michael Greller, Spieth's caddie, after Spieth's bogey save from an adjacent driving range on No. 14.
Spieth looked to have blown another major championship when he hit his drive some 60 yards right of the 13 fairway into near oblivion. Those kind of thoughts come into your head on a day like today, when I'm through four holes and I'm thinking 'are we going to go through this again?'. He becomes the youngest Open victor since the great Seve Ballesteros won the title at 22 in 1979.
He took bogey while Spieth calmly two-putted, finishing the job with a tap-in and hugging his caddie Michael Greller, whom he credited with keeping him rolling through the difficulties of the front nine today. "It's a career goal", Spieth said.
Spieth's dramatic victory at the 146th Open Championship channeled Brady's Super Bowl LI comeback against the Falcons.
"I feel like three years has been too long but at the same time I'm not going to rush it, I'm not going to stay impatient".
Yet Spieth was a shadow of the player he'd been the first three days when he bogeyed three of the first four holes to see his lead disappear.
"This is a dream come true for me, " Spieth said, gazing at his name on the silver claret jug.
"It was more hard to win today that it probably even looked and it probably looked pretty hard", Spieth said. It wasn't, which allowed him to go back in a straight line from the flag until he was on the range among the equipment trucks.
Spieth also completed the third leg of a career slam, having already won Augusta Masters and US Open earlier. Around 20 minutes after finding his ball, Spieth eventually hit his third shot short off the green, chipped to seven feet and holed out for an unlikely bogey.
"There is an excitement and a thrill to have played well, put up a battle, put up a fight, but it's impressive stuff when a guy does something like that". However, in the end, he showed his steely resolve with extraordinary play in the final five holes.
"You've got to be aggressive if you want to win. This was just a completely flipped switch, where I started horribly". He won by three shots - the same margin he started the day with - after a final round 1-under-69.
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But while Spieth held his nerve to register to one last birdie from further out on the last shot of the day, Kuchar lost his. The 2017 Open Championship is down to its final round and Jordan Spieth is moving himself away from the rest of the field.
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