Adam Scott sizzles, but it's the Scottie Scheffler show

In-form Australian Adam Scott has shot one of the best rounds at East Lake in the Tour Championship only for world No.1 Scottie Scheffler to go one better and move a giant step closer towards lifting the FedEx Cup.

Scheffler started the tournament with a two-shot lead based on his strong season, and then looked dominant as ever on Thursday when he posted a six-under 65 to build a seven-shot lead.

Scheffler had five birdies over his last seven holes on a sweltering afternoon at renovated East Lake to pull away from second-placed Xander Schauffele (70) and Collin Morikawa (66).

In fourth place and seven behind are Scott (66), Sam Burns (67), Wyndham Clark (67), Hideki Matsuyama (70) and Keegan Bradley (69).

"The scoring today is better than I thought it might be," a surprised Scott said.

"Maybe it's because there's no wind. I think if the wind gets up we're really going to struggle but I think there are a lot lower scores than I thought out there.

"I played well and had a good score, so I'm pleased with that. But (I am) just trying to get a feel for the golf course. The greens are so firm and those aprons are so tight, they're like a green even."

Scheffler made birdie from the bunker on the par-5 18th hole with an eight-foot putt and took his spot in the PGA Tour record book with an asterisk. No one has ever led by seven after 18 holes as far back as the Tour keeps such records.

The asterisk is because he was only one shot better than Morikawa and four others, including Scott, who each had a 66.

This is the sixth year of the "starting strokes" format at the FedEx Cup finale. Scheffler was the No.1 seed based on his six PGA Tour victories, which includes the Masters and The Players Championship. He started the tournament at 10-under par and with a two-shot lead over Xander Schauffele, the double major winner and No.2 seed.

This is the third straight year Scheffler has started with the lead. He has yet to win the FedEx Cup and its $US25 million ($A37 million) bonus. And by the sound of it, that wasn't on his mind.

"I wasn't thinking about the lead out there today. There's no reason to. It's the first day of the tournament. It's 72 holes. It's a long time out there to be playing with a lead," Scheffler said.

"I was just focused on staying in my own world and continuing to just try to execute."

He got a quick reminder that a two-shot lead on Thursday - or even on a Sunday - is nothing to celebrate. Schauffele made up that deficit on the opening hole with an eight-foot birdie, while Scheffler made his lone bogey by having to play short of the green from behind a tree.

Scheffler, on the strength of a 35-foot birdie putt at No.7, led by one when they made the turn and then left his fellow Olympic gold medallist in the dust.

Schauffele missed birdie chances at 10 and 11. Scheffler made birdie on the next three holes as Schauffele couldn't find a fairway, which led to him not having any reasonable birdie chances.

Scott, who tied second last week at the BMW Championship, played flawless golf.

The Adelaide-born former world No.1 made five birdies, including three in a row beginning on the fifth, to jump to fourth in the standings.

He is the sole Australian in the 30-player field.