Cameron Smith staged one of the greatest back-nine charges ever witnessed at a major championship, coming from four shots behind to win the 150th British Open on Sunday as Rory McIlroy saw another major slip through his fingers.

Smith, winner of golf's unofficial fifth major, The Players Championship, earlier this year, carded a sensational final round eight-under 64 that included a spectacular run of five consecutive birdies from the turn to become the first Australian to hoist the Claret Jug since Greg Norman in 1993.

The 28-year-old Queenslander also became the first Australian man to claim one of golf's four majors since Jason Day's victory at the 2015 PGA Championship.

"All the names on there, every player that's been at the top of their game has won this championship," said Smith, adding he had no plans to get rid of his famous mullet hairstyle. "It's pretty cool to be on there.

"It really hasn't sunk in yet. I don't think it will for a few weeks."

Smith's winning total of 20-under 268 was one better than playing partner American Cameron Young, who eagled the last for a 65 to finish alone in second while McIlroy, the betting favourite coming into St Andrews, faltered at the finish to settle for third.

McIlroy started the final round tied for the lead with Viktor Hovland four strokes clear of the pack and an end to his eight-year major drought looked in sight as he moved two shots ahead alone in first.

The four-time major winner's conservative game plan had appeared to work to perfection as he carded an error free two-under 70.

But in the end fortune favoured the brave as Smith's go-for-broke approach ended with him being crowned Champion Golfer of the Year.

It was another cruel near miss for McIlroy who now has top-10 finishes in all four of this season's majors, adding a third place at St Andrews to a runner-up result at the Masters and a fifth-placed finish at the U.S. Open.

"I felt like I didn't do much wrong today, but I didn't do much right either," summed up McIlroy. "It's just one of those days where I played a really controlled round of golf.

"I did what I felt like I needed to. At the end of the day, it's not life or death.

"It's one that I feel like I let slip away, but there will be other opportunities."

LOW SCORES

As McIlroy and Hovland set out under overcast skies they no doubt noticed the low scores put up by early starters like Sadom Kaewkanjana of Thailand and Mexico's Abraham Ancer who were in the clubhouse with seven-under 65s.

For Smith and Young the message was received -- the Claret Jug was still within reach.

The world number two had preached patience the entire week and was doing just that as he reached the turn without a bogey, a single birdie good enough to keep him two shots ahead of a trio of challengers -- Hovland, Smith and Young.

Yet while McIlroy was practising patience, Smith was mounting a devastating all-out attack, firing five straight birdies to start the back nine, knocking McIlroy from the top of the leaderboard.

"I sometimes think that being behind on certain golf courses and in certain situations is maybe a good thing," said Smith. "I think it's very easy to get defensive out there and keep hitting it to 60, 70 feet, and you can make pars all day, but you're not going to make birdies.

"I think it was a good thing that I was definitely behind.

"I think my mindset would have been a touch different coming in, especially on that back nine, if I was ahead."

One more birdie at the 18th and all that was left for Smith to do was to wait and see if McIlroy, playing the pair behind him, could eagle the last to force a playoff.

Smith was not celebrating just yet, knowing anything was possible having watched Young roll in a 15-foot eagle putt at the 18th to join him momentarily on 19-under, until he drained his short birdie to clinch the Jug.

The 28-year-old earned $2.5 million for his win but that could be only a small fraction of the fortune awaiting him if media reports are true that he is about to sign on with the big-money Saudi-backed LIV Golf Invitational Series.

LIV Golf has poached several top golfers away from the PGA Tour, luring them to the rebel circuit with multi-million dollar guaranteed contracts.

Smith batted away questions about joining them saying he leaves that business to his team.

"I don't know, mate. My team around me worries about all that stuff," said Smith. "I'm here to win golf tournaments."