Updated

By Steve Keating

LEMONT, Illinois (Reuters) - American Dustin Johnson held his nerve as Briton Paul Casey suffered a back-nine meltdown to claim a one-shot victory at the BMW Championship on Sunday.

After letting major wins at the U.S. Open and PGA Championship slip through his fingers on the final day, Johnson carded a rock-solid two-under 69 on a brilliant late summer afternoon at Cog Hill Golf and Country Club for a total of nine-under 275.

This time it was Casey's turn to a suffer a collapse. Leading by three, the Briton watched in horror as his advantage evaporated with three successive bogeys from the 13th on the way to a 69.

(Writing by Steve Keating, Editing by Ed Osmond)