Only Peter Thomson (1955) and Kel Nagle (1960) had ever lifted the Claret Jug at golf’s spiritual home, Smith breaking a 29-year drought for Australians at the game’s most revered major championship. He joins Thomson, Nagle, Greg Norman and Ian Baker-Finch as the only Aussies to be crowned the Champion Golfer of the Year and does so in its 150th staging.

Four back at the start of the final round, five birdies in succession from the turn fuelled a back nine of 30 in a round of eight-under 64, bettering the previous best of six-under 66 set by Zach Johnson in 2015.

A top-five finisher four times in major championships, The Open was always the one that appeared least likely yet the world No.6 yielded his putter to record-breaking proficiency to post 20-under, beating Tiger Woods’s record of 19-under set in 2000.

History said that a four-shot lead was not an insurmountable deficit on a Sunday at St Andrews and as he left the fifth green Smith had reduced the margin by half.

McIlroy’s matching birdie at five extended his advantage to three, a margin he would maintain until both players reached the back nine.

And that’s when Smith launched his stunning assault on golf’s most revered links.

A 345-yard drive followed by a pitch to five feet moved the Queenslander to 15-under but he was just getting started.

The putter that shattered records on Friday rediscovered its mojo as he holed birdie putts from 16 feet at the par-3 11th, 11 feet at the par-4 12th and 18 feet at the par-4 13th.

Trusting the flatstick from behind the back of the par-5 14th, Smith’s eagle putt only just missed on the right side and when he tapped in for birdie he beat McIlroy to 19-under par.

A dalliance with the right rough led to a two-putt par at 15, a result he repeated from the left rough at 16.

McIlroy’s flirtations with birdies continued to be rejected as Smith moved to the famous Road Hole one clear.

A drive across the Old Course Hotel found the fairway 322 yards away but an approach that came up short left a perilous pitch over the game’s most famous bunker.

The world’s best short game exponent chose the prudent play by putting around to the right of the Road Hole’s pot bunker, converting from eight feet to take a one-stroke lead to the last.

With the eyes of the world on him Smith smashed driver to the front edge of the green at 18 as the crowd behind roared their approval of McIlroy’s brilliant approach to 17.

The Northern Irishman’s birdie try missed by just a couple of inches on the left side, leaving Smith with two putts to push out to a two-shot lead.

Cameron Young’s eagle to reach 19-under added extra intrigue to Smith’s final shot of the championship but his two-foot conversion set McIlroy an unlikely assignment.

McIlroy failed to find the green with his tee shot and when his chip skipped past the hole Smith was officially the Champion Golfer of the Year.