Johnson withstood a fierce early challenge from Smith to close with a four-under-par 68 to finish as a five-stroke winner of the COVID-19-postponed Masters.

Smith and South Korean Sungjae Im both closed with steely 69s – but Johnson deservedly donned the green jacket.

The American’s total was the equal-lowest under-par score in major championship history, while Smith is the first player ever to shoot four rounds in the 60s at the Masters.

The 27-year-old Smith’s 15-under 273 was the best ever by a runner-up.

“That’s pretty harsh to get that record and not win,” three-time Masters winner Nick Faldo said.

Smith said he was unaware he was playing for the history books when, for the second day in a row, he made some clutch pars from tough spots on the run home.

“That’s really cool. I honestly can’t believe it, but I have just got to put it down to scrambling and digging deep,” Smith said.

“There was a few times throughout week where I could have let it slip away, and it didn’t.

“But credit to DJ. He was just too good this week.”

Smith started four shots behind world No.1 Johnson but had cut the lead to two shots by the turn thanks in part to two of the best birdies of his career.

Two-time Australian PGA champion Smith applied the pressure to his counterpart when it looked more likely he was about to fold.

Facing what appeared a certain punch out to, at best, a greenside bunker on the seventh, Smith saw a tiny window up through the tree branches.

He took the gamble and flew the ball onto the green before converting a three-metre birdie.

“I wasn’t here to finish second,” Smith told AAP of his decision to take on the hero shot despite there being plenty of golf left to play.

“Obviously had an option of chipping out but I knew I had to keep the pressure on Dustin.

“There was a small gap up there. The club was pretty good. Just had to hit it really hard and good, and it turned out well.”

Smith then hit a brilliant approach from the pine straw on the par-4 ninth to a metre and nailed the putt to be within two of the lead.

But a bogey on the par-4 11th set him scuttling and, despite another brilliant up and down on the 15th for birdie, Johnson pulled away.

“I felt as though I needed to shoot three or four under on that back nine with the wind the way it was,” Smith said.

“It got pretty tricky out there. I still felt I had a chance after 15. I thought if I birdied the last four… at least make him think about it.

“But it wasn’t to be.”

-AAP