Scott, who lead by four strokes with four holes to play, bogeyed each of them, including the final, when he missed a par-saving eight-foot putt.
Els, meanwhile, drained a 15-foot birdie try on the 18th, wrapping up his fourth major title and second British Open crown in 10 years following his 2002 victory at the Muirfield course.
Els also won the U.S. Open in 1994 and 1997.
He fired 2-under 68 Sunday, finishing at 7-under 273. That was one better than Scott, whose epic collapse left him with a round of 5-over 75.