Spieth’s extraordinary one-under-par 69 overnight, Australian time – featuring three back-nine birdies and an eagle after he’d relinquished his three-shot overnight lead – earned the 23-year-old a tension-filled three-stroke victory at 12-under 268.
Little-known Haotong Li, at six under after a blazing Sunday 63, was outright third at six-under 274, with former champion Rory McIlroy (67) sharing fourth with Rafael Cabrera Bello (68) a further stroke behind.
Australian Marc Leishman finished in a five-way tie for sixth at four under after closing with a stylish 65.
But the day – and the famous Claret Jug – belongs to Spieth.
In adding the Open crown to his 2015 Masters and US Open triumphs, the world No.3 joins the legendary Jack Nicklaus as only the second player to have won three of golf’s four majors before the age of 24.
Turning 24 on Thursday, Spieth will head to next month’s US PGA Championship at Quail Hollow striving to become only the sixth player after Tiger Woods, Nicklaus, Gary Player, Gene Sarazen and Ben Hogan to complete a career slam.
He would be the youngest to achieve the fabled feat – and few will back against him after his latest remarkable display of defiance.
“It’s incredible. It’s a life goal of mine. It’s a career goal,” Spieth said.
“Growing up playing golf, I just wanted to be able to play in major championships and compete with the best in the world, and things have happened very quickly.
“And this is as much of a high as I’ve ever experienced in my golfing life.”
But, for all his steel, Spieth admits his Masters collapse had left him with doubts.
“Before the round, I thought I have a reputation as being able to close, but I was hesitant in saying ‘majors’ to myself,” he said.
“And if it weren’t to go my way today, then all I’m going to be questioned about and thought about and murmured about is in comparison to that, and that adds a lot of pressure to me.
“Today took as much out of me as any day that I’ve ever played golf.”
After dropping three shots during a nervy front nine as Kuchar drew level, worse was to come for Spieth.
A wildly errant tee shot on the 13th evoked memories of last year’s Masters meltdown when Spieth threw away the green jacket with a disastrous quadruple seven around Augusta National’s Amen Corner.
Spieth sliced his tee shot almost 50 metres right, over a tall sand dune near the driving range.
After a lengthy deliberation and consultation with officials, the Australian Open champion ended up taking an unplayable lie and hit his next shot from the driving range – and near a Titleist truck.
The bizarre sequence played out in slow motion as Spieth took more than 20 minutes before hitting his shot.
His blind three iron cleared the dune and ended up in front of a bunker short of the green.
Spieth then pitched up and made a clutch two-metre putt for a bogey that will go down in Open folklore.
Kuchar made par to assume a one-shot lead, but what followed was nothing short of astonishing.
Spieth almost aced the par-3 14th, then made eagle on the par-5 15th and further birdies on 16 and 17 to leave his playing partner and Ryder Cup teammate shell-shocked after a wild three-shot swing.
It was a forgettable Open for the Australian contingent.
A frustrated Adam Scott concedes he lost his swing just when he hoped to be contending for British Open glory.
He had to settle for equal 22nd at even par after closing with a final-round three-under 67 when his three back-nine birdies were too little too late.
Runner-up in 2012 and with four top-10s in the past five years, the 2013 Masters champion and former world No.1 departed Royal Birkdale disappointed not to have been a weekend factor.
“The game is feeling close. It’s a horrible thing to say, but I think my swing got a bit knocked around on Friday,” Scott said.
“It was feeling really great Thursday and Friday it got a bit knocked around and I struggled to really get back in my best rhythm for two days.
“The ball position felt funny because it went so far back in my stance on Friday and then I just felt a little bit different from where it was.
“These are the kind of adjustments that you have to make on the fly at these big events when there’s a little adversity and I just didn’t do quite well enough.
“It’s fun to be here but it’s disappointing when you’re not contending. I’ve had that experience a lot and it’s where I want to be.”
Scott will return to America with a fortnight to find his A game for the season’s final major – the US PGA Championship at Quail Hollow from August 10.
“I’m a really good three-round golfer at the moment. Senior Tour is just calling my name, I think,” he ruefully said.
“It’s four rounds of golf. There’s something not quite in the spot and hopefully I can identify that in the next week and a half before we’re getting ready to go to Akron and the PGA.
“But yeah, my game’s in good shape. I keep finishing OK and I know that’s not far from contending. It’s very little things.
“I’m happy with how my putting has felt after putting so poorly at the US Open, it’s back to a nice spot.
“So for me that’s obviously a huge thing for confidence. If I can just keep my swinging rhythm a little better, I’ll be in great shape.”
And Jason Day can’t get home quick enough after his forecast final-round British Open charge failed to materialise.
“Just a really average week, to be honest. Everything was just average,” the Australian No.1 said after closing with a ho-hum 71 to finish in a tie for 27th at one over for the championship.
A third-round 65 proved the highlight as Day narrowly avoided missing a third straight cut.
The former world No.1 admits he needs to improve his “driving, wedges, putting – yeah, pretty much everything” before next month’s WGC Bridgestone Invitational and US PGA Championship at Quail Hollow.
But he also insists it’s not all gloom and doom.
“I’m a lot closer than a lot of people think,” Day said.
“I feel like I am. Obviously the results aren’t reflecting the scores that I’m trying to achieve.
“But once again, I think I’ve just got to keep busting my butt. I’ve got to stay disciplined.
“If I stay disciplined, it’s going to happen. The motivation will come and go, always.
“But as long as I stay disciplined, good things are going to happen around the corner. So I’ve just got to be patient.”
After breaking through for his long overdue maiden major win at the 2015 PGA Championship, Day finished second in his title defence last year.
“It’s always good to go back to a golf tournament that I’ve had good results in the past,” said the world No.6.
“Quail Hollow is one of those events that I don’t really play too often, but I’ve had pretty good finishes there in retrospect to other tournaments.
“I’m excited about the possibility of getting another shot at winning the PGA.
“I’m getting back home tomorrow night and take a week off of practice and get into the WGC.
“I’ve got two weeks in a row, which is fantastic on two golf courses I love playing on.”
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