Joint overnight leader Rory McIlroy carded a third round of 73 to drop down the leaderboard at the BMW Championship but is still only three shots behind co-leaders Dustin Johnson and Hideki Matsuyama.
McIlroy had five bogeys in his round, including one at the last, to drop back to two over in what is a tightly-packed field in Illinois.
World number one Johnson and Matsuyama both carded a one-under 69 at Olympia Fields to share the lead - and they are the only players under par.
Adam Scott of Australia is in a group of three at one over along with Joaquin Niemann of Chile and Canada's Mackenzie Hughes.
Jon Rahm shot a four-under 66 on Saturday in a round that included only one bogey. That came after he forgot to mark his ball before picking it up at the par-four fifth hole. A one-stroke penalty was the outcome.
