Brooks Koepka birdied three of the final four holes on day one of the season-ending Tour Championship to join compatriots Justin Thomas and Xander Schauffele out in front in the race for the FedEx Cup.
Koepka carded a 3-under 67 to erase the three-stroke deficit on 2017 FedEx Cup winner Thomas, who stumbled to a level-par 70.
Schauffele, who won the Tour Championship in 2017, carded a best-of-the-day 64 to join them on 10-under par.
Rory McIlroy started the round five strokes off the pace but his superb round of 66 moved him to within one shot of the lead on 9-under par.
The 30-year-old had raised his concerns about the new handicap start but went on to shoot four birdies in a four under par round.
"I got off to a decent start," said McIlroy. "To play the back nine in three under and get in with a decent score is very nice. I would have liked to have birdied the last but I'm right there with three rounds to go.
"If I can replicate this round of golf three more times I think I'll have a good chance."
Thomas started the round at 10-under due to his #1 ranking in the FedEx Cup following last week's victory, his first win of the season.
But after progressing to 11-under on the front nine, the American stumbled around the turn and his lead evaporated when finding the water at the par-3 15th en route to a double-bogey.
Thomas responded with a birdie at the last though to move back into a share of the lead.
England's Paul Casey moved from his starting position at two under to end day one on six under par as three birdies on the back nine helped him to a share of eighth place.
The winner of the Tour Championship will win the FedEx Cup and a first prize of $15 million, which equates to just over £12 million.
TOUR CHAMPIONSHIP LEADERBOARD
-10 B Koepka, J Thomas, X Schauffele
-9 R McIlroy
-8 M Kuchar, P Cantlay
-7 H Matsuyama