World No 1 Scottie Scheffler saw his lead in the race for the season-ending Tour Championship and FedEx Cup title cut to four strokes after Collin Morikawa fired a superb 63 in Friday's second round at East Lake.
Scheffler, who began the season finale on 10-under, an advantage reflecting his top spot in the FedEx Cup standings, now sits on 21-under after his 5-under 66.
The Masters champion had begun the day with a seven-stroke lead but it was not only Morikawa who closed the gap ahead of the weekend.
Xander Schauffele bounced back from his disappointing 70 in the opening round, to card 64 and move within five strokes of Scheffler.
Scheffler was as solid as ever with five birdies, his sole blemish coming on the par-4 13th where he found two bunkers before missing a nine-foot putt for par.
The American was happy with his performance even if he felt he had been unlucky on the greens.
"I feel like my swing is in a good spot. I've hit it nice last couple days. Really felt like I've hit a lot of lips on the greens, but hitting a lot of quality putts," he said.
"Today the putts that did not go in did not – a lot of them did not miss the cup by very much. A lot of quality stuff out there, and I'm in a good spot going into the weekend," he added.
But while the handicap system gives Scheffler a buffer of protection from his rivals, Morikawa appears determined to push the favourite all the way.
The American reached the turn 4-under and while he bogeyed the 11th he bounced back with birdies on the 13th and 14th.
A late suspension of play for a storm warning threatened to disrupt his momentum, but Morikawa came out and birdied the last two holes to send a clear message to Scheffler.
"For me, it's just bringing energy and just kind of staying alive out there. I've got a game plan that I've set out, and I'm really going to stick to that, just knowing that we've got two more rounds left of the season," he said.
Being paired with Scheffler allowed Morikawa to see his rival close-up but he said he remained focused on his own task.
"He's such a good player that you just know he's going to keep going low and making birdies. I saw that firsthand. I've seen it for years. For me, it's just keep my foot on the gas," he said.
Schauffele put his Thursday struggles out of mind as he produced a bogey free round and came back out in the late evening, after the delay, to make birdie on the last.
"It was better. It was nice to finish off with two big putts. Pretty dark out, so happy those two went in. Keeps the momentum from what was a pretty good round," said this year's British Open and PGA Championship winner.
Schauffele said that Scheffler's lead meant there was no room for caution.
"(Scottie's) been killing everyone at that all year. I know he's not going to let up, so there's only one way to get him," he said.
Australian Adam Scott and American Sahith Theegala and Wyndham Clark are all tied in fourth place on 12-under, nine behind Scheffler.
Clark said there was no question of giving up the chase.
It's going to be very tough to catch up with him. He'd have to not play his best and I'd have to play unbelievable.
"I'm still chasing after that top spot, but I need some help. But a good round tomorrow, if I go shoot something 6-, 7-, 8-under, maybe he shoots even par and we're right in it," he said.