The Englishman found himself 4-0 down in the final, yet still managed to produce a stirring comeback to deny Rodriguez his first senior PDC title.
Humphries maintained his average above 96 throughout the event as he powered to a third straight European Tour crown and £25,000 in prize money.
"In my mind it was probably one of the greatest finals we've seen in the PDC, that's how it felt," said Humphries following his scintillating win.
"I'm over the moon, but credit goes to Rowby-John. He was fantastic. He threw absolutely everything at me.
"When you make your first final, it's not supposed to be as easy as that, and he made it look easy.
"Eighteen months ago I'd have probably lost that 8-2 or 8-3, but I never give up. That's probably my greatest win ever."
Humphries dropped just seven legs on his way to the final after beating Cameron Menzies 6-4, Lukas Wenig 6-2, Ian White 6-1 and Stephen Bunting 7-0.
The PDC European Tour now enjoys a brief hiatus before the Hungarian Darts Trophy takes place in Budapest from September 2-4.
However, the PDC ProTour action continues with Players Championships 18-21 next week, as the race for Betfred World Matchplay qualification concludes from July 8-11.