Joondalup caused the upset of the WA Rugby League premiership on Saturday stunning South Perth 38-22 at Admiral Reserve, Heathridge.
The previously unbeaten Lions conceded four tries in 11 minutes in the second half and never recovered.
After racing to an early 10-0 lead, the Giants lost their composure, with handling errors crippling their play.
Jon Phipps led the Lions fight back to take an 18-10 lead but the Giants, with Macey Howarth in superb form, stormed home.
In other games Willagee Bears ran out 30-22 winners over Rockingham Sharks at Franklin Offshore Sporting Complex and Fremantle Roosters scored a 58-8 win against Kalamunda Bulldogs.
1. South Perth 23
2. North Beach 17
3. Fremantle 14
4. Joondalup 14
5. Willagee 14
6. Rockingham 12
7. Kalamunda 9