Needing to win to supplant Scottie Scheffler from the top of the rankings, Smith never recovered after receiving a retrospective two-stroke penalty at the PGA Tour's opening Playoffs event in Memphis.

Smith ultimately finished in a tie for 13th at nine-under-par, six strokes behind Zalatoris, who denied Austrian Sepp Straka on the third hole of a wild sudden-death playoff at TPC Southwind.

“It was a grind. This week, didn't have my best stuff on Thursday and just kept telling Joel, just keep waiting till the weekend, and to kind of see that decision pay off at the last was pretty cool,” Zalatoris said of the win.

Smith's hopes were all but scuppered even before he teed off on Sunday, after officials docked him two strokes for playing a ball from the wrong place on the 4th hole in round three.

After finding the water on the par-3, the Australian took a drop and incorrectly played his third shot with his ball touching a hazard line.

RIGHT: Adam Scott was the best of the Aussies in Memphis after a Sunday 66. PHOTO: Andy Lyons/Getty Images.

Officials handed Smith the penalty after the recently crowned Open Champion admitted to being unaware he wasn't allowed to play the ball with it touching the red line.

Instead of starting Sunday two shots behind JJ Spaun, Smith began four strokes back at nine-under in a tie for 14th.

He never looked like bridging the gap as Zalatoris shot to the top of the FedExCup standings with his first PGA Tour victory. Smith slipped from second to fourth ahead of this week's BMW Championship.

“Just got to keep doing what we're doing,” Zalatoris said of taking top spot with two events remaining. “I said that before this first win and obviously the process, we've been close and to see it finally pay off has been awesome.”

Countryman Adam Scott carded a fine final-round four-under 66 to finish tied fifth at 11-under and vault from 77th to 45th on the FedExCup leaderboard to seal his place in the second Playoffs event.

Fellow Australians Cam Davis, Lucas Herbert and Marc Leishman also made the 70-man cut for the BMW Championship.

Davis matched Scott's closing 66 to share 13th with Smith and climb to 56th in the FedExCup race.

Leishman (68) scraped in at 68th spot after finishing joint-64th at one-under.

Herbert is 54th in the standings after missing the cut, while Jason Day's season is over.