Willett, who finished on 18-under-par 270, all but sealed the triumph on the front nine, a sensational start with three birdies in the first five holes seeing him leap ahead of overnight leader Luke Donald.
In an all-English final three-ball, Donald faded to third on 12-under-par after struggling to a one-over-par 73, while Ross Fisher claimed second after a fine four-under-par 68 left him on 14-under.
Willett displayed a golden touch around the greens, making birdie putts from the fringe on the third and fifth holes, chipping delightfully from the fringe to set up birdie on the par-five second, and producing excellent bunker-shots to save par on the sixth and 12th holes, while a crucial moment came on the par-five 14th when a brilliant bunker shot left him with a crunch five-foot putt for birdie. After pulling away when a fly landed on his putter, Willett drained the putt to maintain a three-shot lead with four to play, Fisher and Donald both also picking up birdies at the infamous “love-grass hole”.
It was an utterly frustrating day for Donald, the former world number one trying to return to previous heights. On his 37th birthday, he bogeyed the third and fifth holes, which Willett birdied, resulting in a pair of two-shot swings.
Birdies on the sixth and ninth holes brought Donald back into contention, but he was still beholden on mistakes from Willett, which never came despite the 27-year-old’s aggressive play.
Instead, it was Donald who immediately faltered on 10, his drive going into the fairway bunker and his second not going anywhere, as he dropped another shot.
Fisher dropped three shots in his round, his second coming up short of the green on the fifth hole, a wayward drive leading to a bogey on six and another tee-shot into the trees on 11 also costing him. He did birdie 13and 14, but Willett was unstoppable.
The former world amateur number one reached the 17th, with its prize car no longer glistening as storm clouds shut out the sun, and promptly rolled in a 15-foot putt for birdie.
The Yorkshireman from the industrial city of Sheffield had the steel that counted on the final day, a top-class performance bringing him his second European Tour win, but his biggest every paycheque of $1.25 million.
It was a thunderous display to match the thunder that greeted his final putt on 18, a third English winner of the Nedbank Golf Challenge being crowned, joining former world number ones in Lee Westwood and Nick Faldo.