Aaron Davies (2), Rick Ravey and Gary Dixon were Hawks scorers as the Warriors fell to their first ENL defeat since January 2010.
Slough Jets bid to retain their play-off crown started well as they swept to a 4-2 road win over Peterborough Phantoms but 2nd leg goals from Jeff Glowa and Maris Ziedins took the tie into overtime.
Just a minute into the sudden death period Tom Carlon’s stunning strike sent the Phantoms through to the final four weekend.
The final match-up featured MK Lightning and Basingstoke Bison with Lightning running out 7-5 winners on aggregate.
The semi-finals see Phoenix face Lightning while the Phantoms will battle Flames for a place in the final.
Devils surged into a two-goal lead thanks to Jon Pelle and Craig Weller before David-Alexandre Beauregard pulled one back for the Panthers.
Ryan Finnerty’s fierce one-timer made it 3-1 only for Matthew Myers and Jeff Heerema to bring Nottingham level.
Brad Voth put Cardiff back in front but the Panthers refused to lie down. Billy Ryan grabbed the equaliser before Beauregard won it with a sensational strike from the narrowest of angles.