Collin Morikawa created major history at Royal St George’s as he celebrated his Open debut with a magnificent two-shot victory over Jordan Spieth.

Morikawa, winner of last year’s PGA Championship in only his second major appearance, held off riveting challenges from Spieth and Jon Rahm to become the first player in history to win two different majors at the first attempt.

The ultra-composed 24-year-old fired a bogey-free 66 to claim victory on 15 under par, with Spieth’s 66 earning him a runner-up place while Louis Oosthuizen suffered more major heartbreak as he stumbled to a closing 71 and had to settle for a podium finish on 11 under with Rahm.

Seeking to emulate the debut victory of 500/1 outsider Ben Curtis on the Sandwich links 18 years ago, Morikawa began the final round one shot behind Oosthuizen and soon found himself tied at the top when the South African pulled his approach to the fourth and was unable to save par.

Spieth dropped shots at the fourth and sixth only to launch himself back into the running with a brilliant eagle at the seventh, where there was a two-shot swing in the final pairing when Oosthuizen thinned his bunker splash-out across the green and took six, while Morikawa broke his run of pars with his first birdie of the day.

Knowing he now had a two-stroke advantage over his playing partner, Morikawa resisted the temptation to attempt to protect his lead, and extended it with further birdies at eight and nine to go four clear, although Spieth reduced the deficit to three as he picked up shots at the ninth and 10th, where Morikawa made a clutch par save.

Oosthuizen revived his hopes with a stunning tee shot to the par-three 11th which rattled the pin and set up his first birdie, but Spieth was the man piling the pressure on the leader and the 2017 champion closed the gap to a single shot when he rolled in consecutive six-footers for birdies on 13 and 14.

But Morikawa responded with a nerveless 20-foot putt for a priceless four at the long 14th just as Rahm was in the midst of a spectacular late charge, the Spaniard suddenly reeling off four straight birdies from the 13th and coming within a matter of inches from a hole-in-one at the short 16th.

Rahm’s rally would fall short as the pre-tournament favourite closed with pars at 17 and 18 to complete a 66 and claim the clubhouse lead on 11 under, and Spieth missed a great chance to again reduce Morikawa’s lead as he knocked his approach to 12 feet at the penultimate hole only to read too much break into the birdie putt.

Morikawa’s resolve and composure remained intact as he negotiated 15 and 16 in pars, and Spieth could not make his compatriot’s victory march a little less comfortable as he parred the 18th for a 66 – 13 under par for the week and his best result in a major championship since winning at Royal Birkdale four years ago.

Another cast-iron par at the 17th gave Morikawa the relative luxury of a two-shot advantage to take down the 72nd hole, and after another pure strike found the middle of the fairway, he drilled his second to 25 feet before soaking up the applause from the bumper galleries with victory a mere formality.

Two putts later it was official, and an appropriate result in a year of historic major outcomes, while Oosthuizen was left to reflect on yet another case of what might have been as he parred the last four holes to earn a share of third with Rahm, the man who pipped him to the US Open title last month.

Brooks Koepka had earlier threatened the course record when he raced to five under for the day with a third of his final round remaining, but he was disappointed to close with six straight pars for a 65 which left him seven shots behind the champion.

World No 1 Dustin Johnson returned a 67 to finish on seven under along with rising Scot Bob MacIntyre, who secured back-to-back top-10 finishes in both his Open appearances with a 67 that could have been a couple lower had he not pulled his tee shot at the 14th out of bounds.

After two years in possession of the Claret Jug, Royal Portrush champion Shane Lowry’s stout defence of the title ended with a 69 and a creditable tie for 12th place on six under par.