FINAL LEADERBOARD: -11 R Johnson (Swe) -10 R Echenique (Arg)
-9 E Molinari (Ita) -8 B Rumford (Aus), M Brown (NZ), L Oosthuizen (SA)
Selected other: -3 M Hoey (NI)
Johnson was aided by colourful local character Anders Timell as caddie
Home favourite Richard S Johnson birdied the final hole to win the Scandinavian Masters by one shot.
The Swede, 33, carded a 71 to finish 11 under, edging out Rafael Echenique and sealing his third professional title, his first European victory since 2002.
Ryder Cup hopeful Edoardo Molinari was one stroke further back after a 69 with Open champion Louis Oosthuizen carding four bogeys in a 73 for joint fourth.
Joint overnight leader KJ Choi suffered a quadruple bogey nine and was 13th.
On another dark and dismal day in Stockholm, placings were allowed on the fairways at the Bro Hof Slott course because of torrential overnight rain that caused the start of the final round to be delayed.
Despite missing a makeable birdie putt on the opening green, Johnson, based in America on the PGA Tour, found himself with a two-shot lead after Choi made a double bogey and the Korean went on to surprisingly slump to a 78.
Oosthuizen missed a par putt of barely a foot, then bogeyed the fourth after finding a greenside bunker, and dropped another shot at the fifth after a wayward approach as his heroics at St Andrews only a week earlier understandably began to catch up with him.
The major progress was being made by James Morrison, who holed a remarkable long bunker shot for an eagle at the ninth to turn in six- under-par 30 and reach seven under.
Astonishingly the 25-year-old from Surrey then hit the hole again with a chip from around the green on the next, but this time it stayed out and he finished with a round of 67, holing a 20-foot putt at the last for a par to finish on six under.
Johnson and Echenique tussled for the lead but the Swede went ahead again with a six-foot birdie putt at the 15th, prompting a jubilant burst of song from his colourful Dennis Wilson lookalike caddie Anders Timell, a local restauranteur and radio host.
Echenique, the 25-year-old Argentine seeking his first title, escaped with a par at the 17th after his tee shot perched on the edge of the rough down the slope at the island green, and found himself in a share for the lead again when Johnson missed from seven feet for par at 16.
Johnson played a superb shot to five feet at the treacherous par-three 17th, completely surrounded by water, but missed the putt, but with a play-off looming he holed from 20 feet to claim the title and cue the celebrations amongst his home crowd.
Meanwhile, Molinari's third place was not quite enough to depose Luke Donald from the top nine automatic places in the European Ryder Cup table, which is decided at the end of August.
The Italian is now two-and-a-half points behind Donald on the world points list, from which the top four players qualify, and 10th on the European list which offers places to five more players.