Sept 11 Dustin Johnson recovered from a faltering start in the final round, roaring back to clinch a three-stroke victory at the BMW Championship in Indiana on Sunday.
It took only three holes for Johnson to give up his three-shot lead to Casey but four birdies in the next five holes paved the way for the American's 12th victory on the PGA Tour.
The U.S. Open champion continued the best year of his career, carding 67 to finish at 23-under-par 265 at Crooked Stick in Carmel.
Englishman Casey also shot 67 for second place on 20 under, with American Roberto Castro (67) another three shots back in third place. Johnson finished 11 strokes clear of fourth place.
Johnson jumped to top spot on a FedEx Cup points list as the top 30 players advance to the season-finale Tour Championship in Atlanta in two weeks. (Reporting by Andrew Both in Cary, North Carolina; Editing by Clare Fallon)