Scottie Scheffler and Xander Schauffele have broken away from the field after two rounds of the Tour Championship, with Scheffler at 19 under and Schauffele the only player within six strokes, sitting at 17 under.
Scheffler, the world number one, started the season's final event at 10 under due to finishing atop the FedEx Cup standings, and he established a five-stroke lead in his first trip around East Lake Golf Club with a five-under 65.
He was strong again on Friday to post a bogey-free 66, but his lead was trimmed by three shots as second-placed Schauffele produced six birdies and an eagle with one bogey to shoot 63, one shot off the round of the day.
The 18th hole could end up being a turning point in the event, as Scheffler opted to play it safe on the par five while Schauffele decided to take on the water to make the green from his second shot. It resulted in a two-stroke swing as Schauffele eagled the last, cutting the deficit in half from four shots to two.
Only three players posted Friday scores better than 65, with Jon Rahm flying up the leaderboard into outright third place at 13 under after his 63. His eight birdies were the most in the round.
The rest of the field is at least seven shots back from the lead, with Patrick Cantlay and Im Sung-jae tied for fourth at 12 under, Joaquin Niemann alone in sixth at 11 under, and Rory McIlroy has sole possession of seventh at 10 under.
The round of the day went to Max Homa, who went bogey-free with six birdies and an eagle to post a 62 for the best 18 of the tournament so far.
After five birdies from his first eight holes, Homa rattled off seven pars in a row, before a birdie on 16 and an eagle on the last.
Matt Fitzpatrick was Thursday's top performer, but he struggled to a 71 in his second trip around the course, and he is tied at eight under in a group that includes Justin Thomas.
Cameron Smith also shot 71 to drop a shot back to six under, where he is joined by Jordan Spieth, Hideki Matsuyama and Collin Morikawa.