U.S. Open champion Dustin Johnson ran off four birdies in his last five holes Saturday for a 4-under 68 and took a three-shot lead into the final round of the soggy BMW Championship.

Paul Casey did his best to stay with him. Casey, coming off a runner-up finish last week in the FedEx Cup playoffs, matched two of Johnson's birdies during his late run for a bogey-free 68.

Johnson ended with an 18-foot birdie putt that put him at 18-under 198. He will be going for his third victory of the year and move to the top of the FedEx Cup going into the finale at the Tour Championship.

Roberto Castro, tied with Johnson going into the third round, didn't make a birdie in his round of 74.