Van Gerwen started strong and won the first leg but 'Cool Hand' soon stormed back, taking the next eight legs in a row to secure a convincing victory on a humbling night for the Dutchman.
Englishman Humphries' incredible performance included an average score of 112.66, the second-highest ever recorded in a European Tour final.
He also landed two high checkouts, including a phenomenal 170 in the eighth leg.
"I was just unbeatable there to be honest and I'm really, really proud of the way I've played this weekend," Humphries told the PDC after his win.
"That's the level you have to be to win nowadays.
"I felt a little bit tired against Gezzy but I kept going and that final against Michael felt effortless, it felt good.
"To put in performances like that in finals is obviously really pleasing but for me pick up another European Tour title two years on since my first is really special."
"The crowd have been absolutely amazing for me, it's something that I'm not used to but I really appreciate it - it meant a lot."
Humphries, who received a first-round bye, battled through the tournament, defeating players including Luke Woodhouse, Ryan Joyce, Danny Noppert, and Gerwyn Price on his way to the final.
This victory marks Humphries' sixth European Tour title, while Van Gerwen - despite reaching a record-extending 48th final - fell short as his form continues to take a slight dip.
"It's a good time for myself to (reach) the final," said Van Gerwen after the loss.
"Of course, there's a lot of negatives but also a lot of positives and my form I think has come from far - to reach the final I think is a big positive.
"I want to say thank you to the crowd, thanks for the organisation - I think it was a good tournament and I'm pleased.
"You need to perform really well if you want to beat him, we all know that. Early doors in the game I had a few chances but my scoring wasn't good enough and fair play to him.
"I think at this moment he is the best player and we all have to face it, we have to battle but he also knows this is not going to run forever. He's playing some cracking darts, I have to admit that."
Young gun Luke Littler, fresh from winning his first outright night in the Premier League last Thursday in Belfast, didn't qualify for the German event.
All three players, Humphries, Van Gerwen, and Littler, will be back in action on Thursday for night ten of the Premier League in Manchester.
