The American's win capped off a PGA Tour season that saw him return to the top of the world rankings.

The final event of the 2019-20 season looked poised for a drama-free finish with Johnson starting the day with a five-stroke cushion at East Lake Golf Club.

But the 36-year-old American needed almost all of it, carding a final round two-under 68 to fend off 2017 FedExCup champion Justin Thomas and Xander Schauffele, who both closed with rounds of four-under 66.

Johnson, who began the week at 10-under as a result of the Tour Championship's FedExCup scoring system, finished with a winning total of 21-under 269 to earn his 23rd career title and third this season, all coming after the COVID-19 restart.

Johnson is presented with the Calamity Jane trophy. PHOTO: Kevin C. Cox/Getty Imag-es.

"The guys gave me a good fight today," Johnson told the Golf Channel.

"I wanted to be a FedExCup champion, it's something in my career I would like to be and I'm very proud of the way I've played, especially over the last four tournaments."

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Thomas and Schauffele scooped $4.5m (AU$6.2m) each for their share of second while Spain's Jon Rahm also had a final round 66 to finish alone in fourth at 17-under to take home $3m (AU$4.1m).

Australian's Cameron Smith (tied 24th) and Marc Leishman (29th) finished well back in the elite 30-man field but still boosted their bank balances to the tune of $450,500 (AU$620,000) and $405,000 (AU$555,000) respectively.

Smith shot a 71 on Sunday to be even for the week while Leishman's 69 left him at two-over.