After his victory in last year's U.S PGA, the 24-year-old, remarkably, didn't drop a shot over the last 31 holes at Sandwich and holed four birdie putts in a flawless 66 on Sunday to fend off a thrilling challenge from his American compatriot Jordan Spieth.

"This is by far one of the best moments of my life," Morikawa told the returning throng surrounding the 18th green as he clutched the Claret Jug.

Morikawa nails his tee shot at the par-3 16th hole. PHOTO: Getty Images/AFP.

In the baking sunshine on the Kent coast, nobody could have looked cooler than the seemingly nerveless Morikawa.

Apparently, though, it was all an illusion. "I'm glad I look calm because the nerves are definitely up there!" he smiled later.

"But you channel these nerves into excitement and energy, and that puts you away from like a fear factor into 'this is something I want!'.

Morikawa put together rounds of 67, 64, 68 and 66 to lift his second major trophy, finishing two shots ahead of 2017 Open Champion Spieth, with a 15 under par total of 265.

That beat Greg Norman's 72-hole record on the Kent links back in 1993 when he was the last Australian to win the title.

Morikawa, who's been a professional for barely two years, carved out his triumph with an extraordinarily composed Open debut, just like his assured PGA bow at Harding Park 11 months ago.

The Californian became the first man since the late, great Bobby Jones to win two titles in his first eight majors and he's the first to win two on his debut at the event.

Job done ... Morikawa celebrates after tapping in for his par on the 72nd hole. PHOTO: Getty Images.

Spieth threw everything at Morikawa with an eagle at the 5th and four other birdies, but a couple of dropped shots early in his round proved costly in his four under 66.

It was, however, enough to ensure he overhauled Morikawa's final round playing partner Louis Oosthuizen, who had led the tournament from the start and was a shot clear going into Sunday's round.

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There was more heartbreak for the South African, who had finished runner-up in six majors since his 2010 triumph.

Exactly 11 years to the day since he won at St Andrews, Oosthuizen's hopes of a rare wire-to-wire win collapsed as he could only shoot a one over par 71.

The South African finished tied third on 11-under alongside Spaniard Jon Rahm, who carded a 66.

The eerie thing was that, as soon as he surged into a two-shot lead at the par-5 7th, smoothly holing a birdie putt while Oosthuizen knifed one bunker shot straight into another trap to drop a shot, there never felt a moment when Morikawa wasn't in control.

The new Open Champion salutes the Open crowd moments after clinching the win. PHOTO: Getty Images.

After three straight birdies going into the turn, he made nerveless par saves at the 10th and the 15th and when he came down the 18th with a two-shot lead, he was the model of calm as he secured his regulation par and could afford a beaming smile.

"I tell everyone I'm not the biggest history guy, but I want to make memories for myself and to be holding the Claret Jug is one of the greatest memories in my lifetime," he said.

How had he managed to win two of the biggest prizes in the sport at the first attempt?

"I wish I had an answer – and if I did I wouldn't be telling you!," he laughed.

Any hopes of a late Norman-like Australian charge from Cameron Smith, though, disappeared amid three double bogeys for the Queenslander in his final round of 74, which saw him end the tournament on two-under par in joint 33rd place.

Adam Scott, the only other Aussie to make the cut, tied for 46th after his final round 68.

– Ian Chadband