http://www.word-detective.com/2009/04/fluke/
Unfortunately, no one has ever been able to pin down the exact origin of this “fluke,” although within a few years after its first appearance it was being used outside the billiards hall to mean simply “a stroke of good luck” (“Whose run-away horse he had stopped …by the merest fluke,” 1889)
鬼佬都check 唔到個來源