A three-stroke leader at the start of the final round, a middling front nine and two weather delays threatened to disrupt his march to a hometown win in Brisbane and a fifth victory for 2022.

When the resumption of play at 3.10pm lasted just eight minutes, Smith used caffeine to replenish his waning energy levels but it was the presence of his nan Carol – and father Des’s birthday – that would drive the 29-year-old to victory with a final round of three-under 68 and 14-under total.

Shortly after accepting the Joe Kirkwood Cup for a third time from Queensland Premier Annastacia Palaszczuk, Smith choked up as he spoke of the strength and courage showed by his nan who walked all 72 holes – including a seven-hour Sunday round – despite two recent chemotherapy treatments.

For a young man still growing accustomed to the attention and obligations that come with superstardom, it was a potent reminder that there is always more gas in the tank.

“I can’t believe she did it,” said Smith, the champion also in 2017 and 2018.

“Everyone at the start of the week was telling her to pace herself and she was out there all day every day, so it was pretty amazing. Definitely inspiring.

“I don’t know how she did it, but it was also my dad’s birthday as well. After I got back to the tie for the lead there after 11, I really wanted to do it for those two.

“When we went in for that second time, I think I was just really tired. I came in, had a coffee, tried to get some energy back in me and went out there and played really solid the last seven or eight holes.

“It was kind of nice to know that I can do that with not much in the tank.”

It was after the first weather delay at 1.25pm that Smith returned to the course with a one-stroke lead.

The fairytale suddenly shaped to have a nightmarish ending when he made bogey at the par-3 11th, the charging Ryo Hisatsune (65) and resurgent Jason Scrivener (67) suddenly looking to flip the script.

But as he did on the 17th hole at both THE PLAYERS Championship and The Open at St Andrews, it was a remarkable show of short game prowess that would prove the catalyst to his three-stroke win.

A scrappy tee shot at the short par-4 12th left Smith with a steep embankment and a tree between his ball and the flag.

Hours earlier he would have opted for a route closer to the ground but with casual water collecting in the swale, wielded his wedge with imperious precision to set up a birdie from four feet and a lead he would not again relinquish.

“I probably would have hit it underneath the tree if it wasn’t for all that rain,” Smith conceded, his attention now turning to a final flourish at next week’s ISPS HANDA Australian Open.

“There was a bit of casual water down the bottom of the hill, so it was kind of my only option.

“If it hits that water, obviously it stops pretty quick and can turn into four or five pretty quick.”

As Smith fought through fatigue, Hisatsune and Scrivener played with the freedom that comes as a member of the chasing pack.

The 20-year-old from Japan started his round birdie-eagle to thrust his name forward while Scrivener responded to a disappointing Saturday 74 with eight birdies in a round of four-under 67.

Scrivener trailed by just one when he stood on the 17th tee but a disastrous putt from the front of the green that peeled off and into the right bunker led to a double bogey that ended his hopes.

He responded with a birdie at the last to earn a share of second and start his DP World Tour season in strong fashion.

“It’s a tough one to take,” said Scrivener, the 36-hole leader.

“I felt like I had some good momentum, just the putt on 16, I felt like that was probably my chance there, to apply a bit of pressure.

“All in all, tied second is a pretty good start to the season.”

Englishman John Parry matched Hisatsune and Geoff Ogilvy for round of the day with a six-under 65 to earn a share of fourth with Min Woo Lee (69) while West Australian Connor McKinney received the Kel Nagle Plate as low rookie in his first start as a professional.

Click here for final scores and prize money.