Littler, whose staggering progress to the final has captured the imagination of the British public, was one dart away from a 5-2 lead in the best-of-13 set final.
But the 28-year-old world number one Humphries stormed back with a succession of 180s and clinical checkouts to reel off five successive sets and claim a 7-4 victory.
Littler had been attempting to become the youngest ever world darts champion.