The South African had a third-round total of 199 (14 under par), three strokes ahead of Jeff Maggert, who finished second to Els last year and was one of the four contenders for the previous weekend's US Open title.
Els won the Buick by eight strokes last year and after 12 holes of the third round he was eight strokes ahead of the field. However, he lost two strokes coming in, while Maggert picked up three more over the last five holes to record a 66.
Els looked uncatchable after he birdied two of the hardest holes, chipping in on the 11th and sinking a five footer on the 12th. Tiger Woods birdied the last two holes to shoot an even-par 71. He has had just one round under par in his last three tournaments.