The Spaniard, who has slipped down the sport's pecking order and was seeded 10 after a year of injury and below-par performances, fell 7-5 3-6 6-4 6-4 as Brown, ranked 102 in the world, unleashed a barrage of thunderous serves and ground strokes, mixed with clever drop shots to seal a shock victory.
Brown, who had beaten Nadal in the pair's only other meeting last year, looked to rush the Spaniard from the start, blasting winners at every opportunity and squeezing Nadal at the net to cut off his options in an unorthodox style that had the Wimbledon crowd in raptures.
Former world number one Nadal, famed for his athleticism, could not find his rhythm among Brown's variety of play, picking up the second set with a flash of his familiar passing shots and a helpful, albeit momentary, easing in his 30-year old opponent's arrow like attack.
But normal service was resumed afterwards as the dreadlocked Brown, who changed nationality from Jamaican to German in 2010, blasted onward to seal victory with his 13th ace of the match.
"You have to play your A game against him. I am fortunate I played him twice on grass, which is my favourite surface," Brown said.