Patrick Reed fired a 67 in Saturday's third round to take a one-stroke lead at The Northern Trust.
Reed sits one shot clear of Abraham Ancer, and two ahead of both Brandt Snedeker - who put together the lowest round on Saturday with a 63 - and Jon Rahm entering the fourth round.
Saturday's final pairing of Dustin Johnson and Jordan Spieth struggled on moving day, shooting matching rounds of 3-over 74. They now sit tied for 10th and 13th, respectively.
The final round at Liberty National on Sunday will determine who qualifies for the BMW Championship at Medinah, with the top 70 players in the FedExCup standings making the cut to play another week.