McIlroy missed a birdie putt on the latter that would have moved him to part of the lead Tour Championship – round one leaderboard (US unless otherwise stated) -10: J Thomas, X Schauffele, B Koepka; -9: R McIlroy (NI); -8: M Kuchar, P Cantlay; -7: H Matsuyama (Jap); Selected others: -6: P Casey (Eng), J Rahm (Spa); -4: J Rose (Eng)
Rory McIlroy carded an excellent round of 66 to move within a shot from the lead at the season-end Tour Tour.
The Northern Irishman started round a five shots off the lead as part of a staggered starting system derived from the FedEx Cup point list of the PGA Tour.
McIlroy, 30, expressed concern about the scoring system, but went on to shoot four birdies in a four under par round.
He reached nine under par general, a shot behind co-leaders Justin Thomas, Brooks Koepka and Xander Schauffele.
Only the top 30 on the FedEx Cup points list of the PGA Tour are eligible for the Tour Championship and their starting scores work on a sliding scale towards the players in the 26th to 30th, starting at par level level.
The final winner takes a prize of $ 15 million (£ 12.2 million) and McIlroy would have shared the lead at night if he had converted a bird-putt in the last two meters.
"I started well. It's really nice to play the nine in three and come in with a decent score," he told Sky Sports.
"I would have liked to do the last birdie, but I am sitting there with three rounds. If I can replicate this golf round three more times, I think I have a good chance."
Thomas started the day at 10 am, ahead of two shots on the field as a result of his standing in the FedEx Cup points list built up throughout the season.
But the American only navigated the East Lake Golf Club course from Atlanta in level par – including a double bogey when he found water on the par-three 15 – to lose his advantage.
World number one Koepka was three under for his round, but it was Schauffele & # 39; s bogey-free round of six under that most stood out to complete a trio of Americans at the top of the rankings .
Paul Casey from England moved from his starting position at two under to the end of a day at six under par because three birdies on the back nine helped him to a share of eighth place.