Even if that means having to beat him.
Johnson powered his way down the fairways and occasionally out of the brutal rough at East Lake on Friday for a 3-under 67, giving him a one-shot lead over Chappell and moving him one round closer to the $10 million FedEx Cup prize.
The U.S. Open champion is on a different level at the moment.
Even on a demanding test like East Lake this year -- only 10 players remain under par -- Johnson is hitting his driver long and straight. His wedge game has gone from a weakness to a strength. A new putter he put in play two weeks ago when he won the BMW Championship is giving him a better feel for alignment.
Small wonder that this was his seventh straight round at 68 or better during the FedEx Cup playoffs.
"The game is never easy. I wish it was," Johnson said. "Obviously, I'm playing good right now. I've got a lot of confidence in my game. Every week, I feel like I bring the same game, which is nice. But I put in a lot of work to get to where I am."
Johnson was at 7-under 133.
Chappell, one of two players at the Tour Championship who has yet to win on the PGA Tour, was just as solid, even if it doesn't look as spectacular. He has made only one bogey in 36 holes, quite a feat on a course where the Bermuda rough is so punishing that balls sink to the ground and sometimes can't be seen from a foot away.
He shot a 68 and will be in the final group of a playoff event for the second time this year.
Kevin Kisner (70) and Hideki Matsuyama (71) were four shots behind, while Rory McIlroy overcame another rough start on the front nine to post a 70. He was in the group five shots behind, which isn't much of a deficit at the halfway point except for Johnson being the one they have to chase.
If nothing else, Johnson all but eliminated nearly everyone not among the top five seeds vying for the FedEx Cup. McIlroy is No. 6 and still has a chance, though he would have to win the Tour Championship and Johnson would have to finish third.
"I need to win, and I just need someone to play as good as Dustin this week," McIlroy said.
Jason Day is out of the picture. The world's No. 1 player withdrew in the middle of a round at the second straight tournament, citing the same nagging back issues that he hopes will be cured by rest.
By Day withdrawing, Johnson won the points-based PGA player of the year award and is likely to win the player vote as PGA Tour player of the year because of his three victories, with perhaps another to follow.
But there is still work ahead of him, and that starts with Chappell.
"I promise you, I'll be watching Dustin," Chappell said. "He's the best player in the world right now, and it's an opportunity for me to see where my game is. There's a golf tournament going on, and I have a chance to win that. That's the ultimate goal. But I also have a chance to see why he's the best player in the world right now, and I look forward to taking advantage of that opportunity."
Chappell has been a runner-up three times this season and keeps running into the wrong guys -- Kisner at Sea Island, Day at Bay Hill and The Players Championship. He also was in the mix at the TPC Boston until McIlroy pulled away.
"It seems I like going against the hot player at the time," he said.
Russell Knox matched the low score of the tournament with a 66 that allowed him to get back under par at 1-under 139, along with Justin Thomas, who is still hopeful of a Ryder Cup pick at the end of the week.
Thomas lost a shot when his ball moved right as he set his putter down behind a short par putt on the 11th hole. The PGA Tour reviewed it on videotape and gave him a one-shot penalty under Rule 18-2, the same penalty applied to Johnson at Oakmont in the U.S. Open.
Thomas disagreed with, but accepted, the penalty. His argument was it was not a flat surface and the greens were running fast
"It's nothing against the rules officials. It's a god-awful rule," Thomas said. "It's very fortunate it didn't cost Dustin a major championship. I hope it doesn't cost me anything. I don't feel like I did anything wrong."
Mark Russell, the vice president of rules and competition for the tour, said, the wind was light and the ball had been at rest "for quite some time."
"And the moment that Justin put his club behind the ball and addressed the ball, the ball moved," he said. "In that situation, the evidence is against the player and he was penalized."
That left him six shots behind Johnson instead of five. Either way, it's a tall order for Thomas or anyone to catch Johnson.