"What a cool way to end the day," Johnson said.

Johnson shot a four-under 66 to finish at 19 under for his second PGA Tour victory this year and 18th of his career to move back to the top of the world golf rankings.

He had held that status for 64 straight weeks before being usurped by fellow American Justin Thomas on May 13.

"It means a lot," Johnson said of reclaiming the No.1 ranking.

"It was a long way to get there, and I held it for a long time and obviously JT took it from me for a little while.

"It was nice to finish like that and get it back."

Johnson finished with the eagle, three birdies and a bogey on Sunday while co-overnight leader Andrew Putnam started the final round with a double bogey on his way to a 72.

Preparing for the US Open, which he won in 2016, Johnson cruised to victory and heads to Shinnecock Hills after stringing together four straight rounds in the 60s.

Johnson plays his second shot on the 12th hole during the final round of the FedEx St. Jude Classic. PHOTO: Andy Lyons/Getty Image

He went 67, 63 and 65 before wrapping up a final round that felt almost like a practice round with the only question remaining how low Johnson would go.

At least until his dramatic walk-off eagle.

Johnson was in the intermediate rough to the right of the fairway, and the ball bounced twice before rolling into the cup to bring fans to their feet.

No player has ever won on the PGA Tour and followed by winning the US Open but Johnson sees no reason why he couldn't be the first.

"I know what it takes," he said.

"I'm going to have to play a lot like I did this week if I want to win next week."

J.B. Holmes (67) was third, 10 shots off the winner at nine under.

Phil Mickelson had a 65 on Sunday and was at six under in a tie for 12th in a group that included Stuart Appleby, who closed with a 69.

His fellow Australian Cameron Percy had a 68 to be tied for 26th at four under while Aaron Baddeley (71) and Matt Jones (73) finished tied for 37th and 51st respectively.