The Pole beat compatriot Tomasz Gollob to the line to win the final in Auckland.
Nicki Pedersen and Australian Darcy Ward took the minor places in the final with Brit Tai Woffinden picking up nine points for finishing joint seventh.
Hampel began with two third places at Western Springs before winning heat 10 and adding two further second place finishes and he went from the outside gate in the first semi-final in which he won.
Gollob won the second semi with defending world champion Chris Holder only third.
With the most points heading into the showpiece, Gollob chose the second start position and it left the inside gate for Hampel who made a great start and coasted to his third GP victory.
The 30-year-old from Lodz had previously won the Danish GP in 2010, when he finished the year second overall, and the Scandinavian GP in 2011.
The second round of the 2013 series is in Poland on April 20 and British fans will be able to watch all the action live on Eurosport.
- Sports & Recreation
- Tomasz Gollob
- Nicki Pedersen
- Darcy Ward