(Reuters) - Dustin Johnson collected his 20th PGA Tour victory in style when he ran away with the WGC-Mexico Championship by five strokes on Sunday.
Johnson carded a closing five-under-par 66 at Club de Golf Chapultepec in Mexico City to claim the World Golf Championships event for the second time in three years.
The lanky American finished at 21-under 263, while Northern Irishman McIlroy shot 67 for second place on 16-under.
McIlroy cut the margin to two shots after three holes, but could get no closer, with six back nine birdies being too little, too late.
Johnson finished 10 strokes clear of third-placed Englishmen Paul Casey and Ian Poulter plus Thailand's Kiradech Aphibarnrat.
Tiger Woods (69) tied for 10th, 13 shots behind Johnson, who started the final round four strokes ahead of McIlroy.
Johnson's second worldwide win in three weeks -- after the European Tour's Saudi International -- lifts him to number two in the world rankings, just behind Englishman Justin Rose.
(Reporting by Andrew Both in Cary, North Carolina; Editing by Ken Ferris)