Jordan Spieth birdied three of his last five holes to grab a three-shot lead after the third round of the Northern Trust.
Spieth began the day in a four-way tie for the lead, but he quickly broke out of that with four birdies in his first eight holes at Glen Oaks Club on Saturday.
Winner of this year's Open Championship, Spieth used a hot putter to separate himself from the rest of the field.
Spieth ultimately shot a six-under 64 to get to 12 under for the tournament, which is the first of this year's FedEx Cup Play-offs.
Dustin Johnson, who also started the day tied for the lead, shot a three-under 67 to get to nine under.
He finished round three with four birdies and one bogey. Johnson, still ranked world number one, has just one top 10 since injuring himself before the Masters.
Jon Rahm (67), Paul Casey (66), Matt Kuchar (68) and Patrick Reed (66) are all tied for third at seven under.
Casey, who often contends but has struggled to get over the hump and win, provided some insight into what he thinks it will take for him to be successful more often.
"Get rid of Jordan [Spieth] and Dustin [Johnson] from the top of the leaderboards," Casey said.
Keegan Bradley (66) is outright seventh at six under, a shot ahead of Kevin Chappell (64) and Justin Rose (69).
Rickie Fowler dropped out of contention after a 74 left him at two under and alongside the likes of Jason Day (68) and Henrik Stenson (67) in a tie for 22nd.
Rory McIlroy continued his recovery with a one-under 69 getting him back to even par.