WASHINGTON (REUTERS) - Thoughts of a Dustin Johnson runaway at the Tour Championship were dispelled when he faltered late to fall back into a tie for the third-round lead with fellow American Kevin Chappell in Atlanta on Saturday.

Johnson, the hottest player in the game coming off a victory, squandered a chance to take a stranglehold on the tournament when he double-bogeyed the par-four 17th, compounding a poor drive by clipping a pine tree with his second shot.

He was on the wrong end of a three-shot swing as Chappell birdied the same hole from 10 feet.

US Open champion Johnson steadied the ship to birdie the par-five 18th for a one-under 69, his eighth consecutive round in the 60s but one that left him ruing what might have been.

"This course is very difficult off the tee and I missed a couple of drives on the back nine and made a couple of bogeys and a bad double bogey there on the 17th," he said before accentuating the positives. "I'm happy with my position. I felt like I played well today. A couple of loose drives and it's easy to make bogeys around here ... so if I make a mistake, I don't let it bother me."

Chappell fired 68 to join Johnson at eight-under 202.

Johnson's stumble let a bunch of players back into the hunt, with Northern Irishman Rory McIlroy (66) and American Ryan Moore (66) two shots behind, and Japanese Hideki Matsuyama (68) three back despite a triple-bogey at the 14th.

Johnson, top seed in the FedExCup standings, will clinch the season-long points race and its US$10 million (S$13.6 million) bonus if he wins the tournament on Sunday.