Jason Dufner took the lead over Lee Westwood with a birdie on the 16th hole and now sits at the top of the leaderboard with a 6-under par score and 3-under for the day.
Peter Hanson, who had tied for the lead much earlier in the round, double-bogeyed on the 11th hold and sits in ninth place at 2-under par.
Rory McIlroy is tied for fifth-place with Fred Couples, Ben Crane and Francesco Molinari, who all sit at 3-under par. Tiger Woods birdied his first hole of the day and is tied in 15th place.
If Dufner were to actually win, it would be only his third PGA Tour win of his career and his first majors victory. Dufner, 35, is a 12-year professional who finished second at the PGA Championship in 2011.