Dustin Johnson moved into the outright lead at the Tour Championship after carding a three-under 67 in the second round.
The American U.S. Open champion sits at seven under at East Lake, a shot clear of countryman Kevin Chappell (68).
The duo have broken away from the rest of the field, with Kevin Kisner (70) and Hideki Matsuyama (71) at three under.
There is also one less contender after world number one Jason Day withdrew, citing back pain.
Johnson, the FedEx Cup leader, made birdies on holes five and six before a mixed back nine, which included two bogeys.
Chappell, who along with Matsuyama shared the overnight lead with Johnson, made a hat-trick of birdies from six to eight before his only blemish at the 11th.
Behind Kisner and Matsuyama are Ryan Moore (68), Englishman Paul Casey (70) and Rory McIlroy (70).
McIlroy recovered from a dreadful start that included three bogeys on his first five holes. His back nine was much better, as birdies on 10, 12 and 17 saw him rescue his round.
Jordan Spieth also slipped back, shooting a two-over 72 to sit tied for 11th at even-par.
At one under are Russell Knox (66), Justin Thomas (71) and Kim Si-woo (72), sitting tied for eighth.