LEMONT, Ill. — Dustin Johnson won the BMW Championship and eased a summer of Sunday disappointments.

Playing in the final group for the fourth time since June, Johnson blasted a tee shot over the trees and into the fairway on the 17th hole at Cog Hill to set up a tap-in birdie and the outright lead. He closed with a 2-under 69 for a one-shot victory over Paul Casey.

It was the second victory this year for Johnson, a 26-year-old American who has quickly emerged as one of golf's rising stars. And it helped ease the sting of lost chances in three other tournaments, including two majors.

He blew a three-shot lead at the U.S. Open. He made up a three-shot deficit at the PGA Championship, only to lose a one-shot lead on the final hole when he didn't realize he was in a bunker and grounded his club.

"To finally get it done, especially after all the things I've gone through this summer ... it can't feel any better," said Johnson, who finished at 9-under 275 and won $1.35 million. "I played really good golf today."

Johnson played bogey-free and was flawless to the very end on the back nine Sunday.

He moved to No. 2 in the FedEx Cup standings, giving him a clear shot at the $10 million bonus in two weeks at the Tour Championship.