The South African claimed his fourth major title and 10 years after his last, when he lifted the Claret Jug in Muirfield in 2002.
British Open: Els wins as Scott blows a four-shot lead
Ten years on from his last major victory Ernie Els became the British Open champion again – and could hardly believe it.
The 42-year-old South African, same age as last year's winner Darren Clarke, triumphed after Adam Scott suffered a nightmare collapse over Royal Lytham's closing stretch.
Scott, chasing his first major, looked all set to become the first Australian to hold the Claret Jug aloft since Greg Norman in 1993 when he led by four shots with only four holes to play.
But he bogeyed them all and Els, having made a 15-foot birdie putt on the final green 20 minutes earlier, suddenly found himself with a fourth major title without even having to go into a play-off.
As Nick Faldo said: "Well done Ernie Els, but Adam Scott is going to be scarred for life."
Els commented: "I'm just all numb at the moment. He's a great friend of mine. Obviously we both wanted to win very badly for different reasons and I really feel for him.
"It's the nature of the beast. That's why we are out here. You win, you lose and it was my time.
"I was hoping at best play-off. When I was on the 17th green he was on the 16th tee and, as we all know, it's not the hardest hole."
Scott, whose caddie Steve Williams won 13 majors with Tiger Woods, had allowed the gap to come down to two by failing to get up and down from a bunker on the 15th.
He then three-putted the next and while playing the 17th would certainly have heard the roar - the loudest of the week - for Els's last green putt for a 68 and seven-under-par aggregate of 273.
The "Big Easy", second at Lytham in 1996 and third in 2001, almost resigned himself to another near-miss. But things were about to change far more than he anticipated.
Scott pulled his approach into the rough, and when he drove into more sand down the last and had to hack out, Els had one hand on the trophy.
His Presidents Cup teammate played a superb third to eight feet, but the par putt to force extra holes was pulled wide and that was that.
Having stood 11 under earlier in the day, he signed for a 75 and six under.
Woods, who also finished poorly in addition to taking a triple bogey, tied for third with fellow American Brandt Snedeker three shots further back, while Scott's playing partner Graeme McDowell ended up fifth with world No 1 Luke Donald.
In his winner's speech Els told the crowd: "I had a lot of support this week. But you guys have got to ask yourselves the question were you just being nice to me or did you actually believe I could win?".
Many thought his best days were long behind him and he did not even qualify for The Masters in April.
* Press Association